diff --git a/.eslintignore b/.eslintignore
index 38a3ebdda2df..00c15aacdd21 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -1,3 +1,6 @@
+# Allow linting of .eslintrc.js files.
+!**/.eslintrc.js
+
 # Always ignore node_modules.
 **/node_modules/**/*.*
 
diff --git a/.eslintrc b/.eslintrc.js
similarity index 84%
rename from .eslintrc
rename to .eslintrc.js
index 491de0d4f26c..9820b70325e7 100644
--- a/.eslintrc
+++ b/.eslintrc.js
@@ -1,4 +1,6 @@
-{
+"use strict";
+
+module.exports = {
   // When adding items to this file please check for effects on sub-directories.
   "plugins": [
     "mozilla"
@@ -9,4 +11,4 @@
   "env": {
     "es6": true
   },
-}
+};
diff --git a/accessible/.eslintrc b/accessible/.eslintrc.js
similarity index 76%
rename from accessible/.eslintrc
rename to accessible/.eslintrc.js
index 102708114c32..3cd32ed6019e 100644
--- a/accessible/.eslintrc
+++ b/accessible/.eslintrc.js
@@ -1,6 +1,8 @@
-{
+"use strict";
+
+module.exports = {
   "extends": [
-    "../.eslintrc"
+    "../.eslintrc.js"
   ],
   "globals": {
     "Cc": true,
@@ -12,4 +14,4 @@
     "Services": true,
     "XPCOMUtils": true
   }
-}
+};
diff --git a/accessible/tests/browser/.eslintrc b/accessible/tests/browser/.eslintrc.js
similarity index 96%
rename from accessible/tests/browser/.eslintrc
rename to accessible/tests/browser/.eslintrc.js
index 4723d7df4c62..61804459098b 100644
--- a/accessible/tests/browser/.eslintrc
+++ b/accessible/tests/browser/.eslintrc.js
@@ -1,6 +1,8 @@
-{
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
   "extends": [
-    "../../../testing/mochitest/browser.eslintrc"
+    "../../../testing/mochitest/browser.eslintrc.js"
   ],
   // All globals made available in the test environment.
   "globals": {
@@ -46,7 +48,7 @@
     "invokeSetAttribute": true,
     "invokeSetStyle": true,
     "invokeFocus": true,
-    "findAccessibleChildByID": true,
+    "findAccessibleChildByID": true
   },
   "rules": {
     "mozilla/mark-test-function-used": 1,
@@ -212,6 +214,6 @@
     "no-void": 0,
     "no-wrap-func": 0,
     "operator-assignment": 0,
-    "operator-linebreak": [2, "after"],
+    "operator-linebreak": [2, "after"]
   }
-}
+};
diff --git a/browser/.eslintrc b/browser/.eslintrc
deleted file mode 100644
index fa8feacbacfc..000000000000
--- a/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../toolkit/.eslintrc"
-  ],
-}
diff --git a/browser/.eslintrc.js b/browser/.eslintrc.js
new file mode 100644
index 000000000000..7194832a7d33
--- /dev/null
+++ b/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../toolkit/.eslintrc.js"
+  ],
+};
diff --git a/browser/base/content/test/alerts/.eslintrc b/browser/base/content/test/alerts/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/base/content/test/alerts/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/base/content/test/alerts/.eslintrc.js b/browser/base/content/test/alerts/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/base/content/test/alerts/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/base/content/test/chrome/.eslintrc b/browser/base/content/test/chrome/.eslintrc
deleted file mode 100644
index 218d988742d2..000000000000
--- a/browser/base/content/test/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/browser/base/content/test/chrome/.eslintrc.js b/browser/base/content/test/chrome/.eslintrc.js
new file mode 100644
index 000000000000..8c0f4f574c28
--- /dev/null
+++ b/browser/base/content/test/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/browser/base/content/test/general/.eslintrc b/browser/base/content/test/general/.eslintrc
deleted file mode 100644
index 001a4910587f..000000000000
--- a/browser/base/content/test/general/.eslintrc
+++ /dev/null
@@ -1,6 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc",
-    "../../../../../testing/mochitest/mochitest.eslintrc",
-  ]
-}
diff --git a/browser/base/content/test/general/.eslintrc.js b/browser/base/content/test/general/.eslintrc.js
new file mode 100644
index 000000000000..11abd6140ecf
--- /dev/null
+++ b/browser/base/content/test/general/.eslintrc.js
@@ -0,0 +1,8 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js",
+    "../../../../../testing/mochitest/mochitest.eslintrc.js",
+  ]
+};
diff --git a/browser/base/content/test/newtab/.eslintrc b/browser/base/content/test/newtab/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/base/content/test/newtab/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/base/content/test/newtab/.eslintrc.js b/browser/base/content/test/newtab/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/base/content/test/newtab/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/base/content/test/plugins/.eslintrc b/browser/base/content/test/plugins/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/base/content/test/plugins/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/base/content/test/plugins/.eslintrc.js b/browser/base/content/test/plugins/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/base/content/test/plugins/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/base/content/test/popupNotifications/.eslintrc b/browser/base/content/test/popupNotifications/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/base/content/test/popupNotifications/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/base/content/test/popupNotifications/.eslintrc.js b/browser/base/content/test/popupNotifications/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/base/content/test/popupNotifications/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/base/content/test/referrer/.eslintrc b/browser/base/content/test/referrer/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/base/content/test/referrer/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/base/content/test/referrer/.eslintrc.js b/browser/base/content/test/referrer/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/base/content/test/referrer/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/base/content/test/social/.eslintrc b/browser/base/content/test/social/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/base/content/test/social/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/base/content/test/social/.eslintrc.js b/browser/base/content/test/social/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/base/content/test/social/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/contextualidentity/test/browser/.eslintrc b/browser/components/contextualidentity/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/components/contextualidentity/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/contextualidentity/test/browser/.eslintrc.js b/browser/components/contextualidentity/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/components/contextualidentity/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/customizableui/test/.eslintrc b/browser/components/customizableui/test/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/browser/components/customizableui/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/customizableui/test/.eslintrc.js b/browser/components/customizableui/test/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/browser/components/customizableui/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/dirprovider/tests/unit/.eslintrc b/browser/components/dirprovider/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/components/dirprovider/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/components/dirprovider/tests/unit/.eslintrc.js b/browser/components/dirprovider/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/components/dirprovider/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/components/downloads/test/browser/.eslintrc b/browser/components/downloads/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/components/downloads/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/downloads/test/browser/.eslintrc.js b/browser/components/downloads/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/components/downloads/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/downloads/test/unit/.eslintrc b/browser/components/downloads/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/components/downloads/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/components/downloads/test/unit/.eslintrc.js b/browser/components/downloads/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/components/downloads/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/components/extensions/.eslintrc b/browser/components/extensions/.eslintrc.js
similarity index 74%
rename from browser/components/extensions/.eslintrc
rename to browser/components/extensions/.eslintrc.js
index 2484d54fc9dc..81a11c4ac67b 100644
--- a/browser/components/extensions/.eslintrc
+++ b/browser/components/extensions/.eslintrc.js
@@ -1,5 +1,7 @@
-{
-  "extends": "../../../toolkit/components/extensions/.eslintrc",
+"use strict";
+
+module.exports = {  // eslint-disable-line no-undef
+  "extends": "../../../toolkit/components/extensions/.eslintrc.js",
 
   "globals": {
     "AllWindowEvents": true,
@@ -17,6 +19,4 @@
     "WindowListManager": true,
     "WindowManager": true,
   },
-}
-
-
+};
diff --git a/browser/components/extensions/test/browser/.eslintrc b/browser/components/extensions/test/browser/.eslintrc.js
similarity index 78%
rename from browser/components/extensions/test/browser/.eslintrc
rename to browser/components/extensions/test/browser/.eslintrc.js
index 7c5300de55c0..7aea41ca76a2 100644
--- a/browser/components/extensions/test/browser/.eslintrc
+++ b/browser/components/extensions/test/browser/.eslintrc.js
@@ -1,5 +1,7 @@
-{
-  "extends": "../../../../../testing/mochitest/browser.eslintrc",
+"use strict";
+
+module.exports = {  // eslint-disable-line no-undef
+  "extends": "../../../../../testing/mochitest/browser.eslintrc.js",
 
   "env": {
     "webextensions": true,
@@ -26,5 +28,5 @@
     "openContextMenu": true,
     "openExtensionContextMenu": true,
     "CustomizableUI": true,
-  }
-}
+  },
+};
diff --git a/browser/components/extensions/test/xpcshell/.eslintrc b/browser/components/extensions/test/xpcshell/.eslintrc
deleted file mode 100644
index 03381914eed7..000000000000
--- a/browser/components/extensions/test/xpcshell/.eslintrc
+++ /dev/null
@@ -1,7 +0,0 @@
-{
-  "extends": "../../../../../testing/xpcshell/xpcshell.eslintrc",
-
-  "globals": {
-    "browser": false,
-  },
-}
diff --git a/browser/components/extensions/test/xpcshell/.eslintrc.js b/browser/components/extensions/test/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..2bfe540ea589
--- /dev/null
+++ b/browser/components/extensions/test/xpcshell/.eslintrc.js
@@ -0,0 +1,9 @@
+"use strict";
+
+module.exports = {  // eslint-disable-line no-undef
+  "extends": "../../../../../testing/xpcshell/xpcshell.eslintrc.js",
+
+  "globals": {
+    "browser": false,
+  },
+};
diff --git a/browser/components/feeds/test/.eslintrc b/browser/components/feeds/test/.eslintrc
deleted file mode 100644
index 9174183fccce..000000000000
--- a/browser/components/feeds/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/browser/components/feeds/test/.eslintrc.js b/browser/components/feeds/test/.eslintrc.js
new file mode 100644
index 000000000000..3c788d6d681c
--- /dev/null
+++ b/browser/components/feeds/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/browser/components/feeds/test/chrome/.eslintrc b/browser/components/feeds/test/chrome/.eslintrc
deleted file mode 100644
index 218d988742d2..000000000000
--- a/browser/components/feeds/test/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/browser/components/feeds/test/chrome/.eslintrc.js b/browser/components/feeds/test/chrome/.eslintrc.js
new file mode 100644
index 000000000000..8c0f4f574c28
--- /dev/null
+++ b/browser/components/feeds/test/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/browser/components/feeds/test/unit/.eslintrc b/browser/components/feeds/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/components/feeds/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/components/feeds/test/unit/.eslintrc.js b/browser/components/feeds/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/components/feeds/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/components/migration/tests/unit/.eslintrc b/browser/components/migration/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/components/migration/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/components/migration/tests/unit/.eslintrc.js b/browser/components/migration/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/components/migration/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/components/newtab/tests/browser/.eslintrc b/browser/components/newtab/tests/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/components/newtab/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/newtab/tests/browser/.eslintrc.js b/browser/components/newtab/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/components/newtab/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/newtab/tests/xpcshell/.eslintrc b/browser/components/newtab/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/components/newtab/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/components/newtab/tests/xpcshell/.eslintrc.js b/browser/components/newtab/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/components/newtab/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/components/originattributes/test/browser/.eslintrc b/browser/components/originattributes/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/components/originattributes/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/originattributes/test/browser/.eslintrc.js b/browser/components/originattributes/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/components/originattributes/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/places/tests/browser/.eslintrc b/browser/components/places/tests/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/components/places/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/places/tests/browser/.eslintrc.js b/browser/components/places/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/components/places/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/places/tests/chrome/.eslintrc b/browser/components/places/tests/chrome/.eslintrc
deleted file mode 100644
index 218d988742d2..000000000000
--- a/browser/components/places/tests/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/browser/components/places/tests/chrome/.eslintrc.js b/browser/components/places/tests/chrome/.eslintrc.js
new file mode 100644
index 000000000000..8c0f4f574c28
--- /dev/null
+++ b/browser/components/places/tests/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/browser/components/places/tests/unit/.eslintrc b/browser/components/places/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/components/places/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/components/places/tests/unit/.eslintrc.js b/browser/components/places/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/components/places/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/components/preferences/in-content/tests/.eslintrc b/browser/components/preferences/in-content/tests/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/components/preferences/in-content/tests/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/preferences/in-content/tests/.eslintrc.js b/browser/components/preferences/in-content/tests/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/components/preferences/in-content/tests/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/privatebrowsing/test/browser/.eslintrc b/browser/components/privatebrowsing/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/components/privatebrowsing/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/privatebrowsing/test/browser/.eslintrc.js b/browser/components/privatebrowsing/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/components/privatebrowsing/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/safebrowsing/content/test/.eslintrc b/browser/components/safebrowsing/content/test/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/components/safebrowsing/content/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/safebrowsing/content/test/.eslintrc.js b/browser/components/safebrowsing/content/test/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/browser/components/safebrowsing/content/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/search/test/.eslintrc b/browser/components/search/test/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/browser/components/search/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/search/test/.eslintrc.js b/browser/components/search/test/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/browser/components/search/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/selfsupport/test/.eslintrc b/browser/components/selfsupport/test/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/browser/components/selfsupport/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/selfsupport/test/.eslintrc.js b/browser/components/selfsupport/test/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/browser/components/selfsupport/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/sessionstore/test/.eslintrc b/browser/components/sessionstore/test/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/browser/components/sessionstore/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/sessionstore/test/.eslintrc.js b/browser/components/sessionstore/test/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/browser/components/sessionstore/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/sessionstore/test/unit/.eslintrc b/browser/components/sessionstore/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/components/sessionstore/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/components/sessionstore/test/unit/.eslintrc.js b/browser/components/sessionstore/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/components/sessionstore/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/components/shell/test/.eslintrc b/browser/components/shell/test/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/browser/components/shell/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/shell/test/.eslintrc.js b/browser/components/shell/test/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/browser/components/shell/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/shell/test/unit/.eslintrc b/browser/components/shell/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/components/shell/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/components/shell/test/unit/.eslintrc.js b/browser/components/shell/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/components/shell/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/components/tests/browser/.eslintrc b/browser/components/tests/browser/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/browser/components/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/tests/browser/.eslintrc.js b/browser/components/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/browser/components/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/translation/test/.eslintrc b/browser/components/translation/test/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/browser/components/translation/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/translation/test/.eslintrc.js b/browser/components/translation/test/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/browser/components/translation/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/components/translation/test/unit/.eslintrc b/browser/components/translation/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/components/translation/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/components/translation/test/unit/.eslintrc.js b/browser/components/translation/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/components/translation/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/components/uitour/test/.eslintrc b/browser/components/uitour/test/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/browser/components/uitour/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/components/uitour/test/.eslintrc.js b/browser/components/uitour/test/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/browser/components/uitour/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/experiments/test/xpcshell/.eslintrc b/browser/experiments/test/xpcshell/.eslintrc
deleted file mode 100644
index 78141af911f7..000000000000
--- a/browser/experiments/test/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/experiments/test/xpcshell/.eslintrc.js b/browser/experiments/test/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..fee088c17903
--- /dev/null
+++ b/browser/experiments/test/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/extensions/formautofill/.eslintrc b/browser/extensions/formautofill/.eslintrc.js
similarity index 98%
rename from browser/extensions/formautofill/.eslintrc
rename to browser/extensions/formautofill/.eslintrc.js
index cacd9c22ed3d..209df44321a5 100644
--- a/browser/extensions/formautofill/.eslintrc
+++ b/browser/extensions/formautofill/.eslintrc.js
@@ -1,5 +1,7 @@
-{
-  "extends": "../../.eslintrc",
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../.eslintrc.js",
 
   "globals": {
     "Components": true,
@@ -333,7 +335,7 @@
     "no-inline-comments": 0,
 
     // Disallow use of labels for anything other then loops and switches.
-    "no-labels": [2, { "allowLoop": true }],
+    "no-labels": [2, {"allowLoop": true}],
 
     // Disallow use of multiline strings (use template strings instead).
     "no-multi-str": 1,
@@ -469,5 +471,5 @@
 
     // Disallow creating new instances of String, Number, and Boolean
     "no-new-wrappers": 2,
-  }
-}
+  },
+};
diff --git a/browser/extensions/formautofill/test/browser/.eslintrc b/browser/extensions/formautofill/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/browser/extensions/formautofill/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/extensions/formautofill/test/browser/.eslintrc.js b/browser/extensions/formautofill/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..52a2004c9d7b
--- /dev/null
+++ b/browser/extensions/formautofill/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js",
+  ],
+};
diff --git a/browser/extensions/pdfjs/test/.eslintrc b/browser/extensions/pdfjs/test/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/browser/extensions/pdfjs/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/extensions/pdfjs/test/.eslintrc.js b/browser/extensions/pdfjs/test/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/browser/extensions/pdfjs/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/modules/test/.eslintrc b/browser/modules/test/.eslintrc
deleted file mode 100644
index a9848783e325..000000000000
--- a/browser/modules/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/browser/modules/test/.eslintrc.js b/browser/modules/test/.eslintrc.js
new file mode 100644
index 000000000000..e2d7896f8d7a
--- /dev/null
+++ b/browser/modules/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/browser/modules/test/unit/social/.eslintrc b/browser/modules/test/unit/social/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/browser/modules/test/unit/social/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/modules/test/unit/social/.eslintrc.js b/browser/modules/test/unit/social/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/browser/modules/test/unit/social/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/browser/modules/test/xpcshell/.eslintrc b/browser/modules/test/xpcshell/.eslintrc
deleted file mode 100644
index 78141af911f7..000000000000
--- a/browser/modules/test/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/browser/modules/test/xpcshell/.eslintrc.js b/browser/modules/test/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..fee088c17903
--- /dev/null
+++ b/browser/modules/test/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/devtools/.eslintrc b/devtools/.eslintrc.js
similarity index 98%
rename from devtools/.eslintrc
rename to devtools/.eslintrc.js
index 58f89febe55d..4d80d5b4426d 100644
--- a/devtools/.eslintrc
+++ b/devtools/.eslintrc.js
@@ -1,4 +1,6 @@
-{
+"use strict";
+
+module.exports = {
   "plugins": [
     "react"
   ],
@@ -150,7 +152,10 @@
     // rule is a better rule to check this.
     "max-depth": 0,
     // Maximum length of a line.
-    "max-len": [2, 90, 2, {"ignoreUrls": true, "ignorePattern": "data:image\/|\\s*require\\s*\\(|^\\s*loader\\.lazy|-\\*-"}],
+    "max-len": [2, 90, 2, {
+      "ignoreUrls": true,
+      "ignorePattern": "data:image\/|\\s*require\\s*\\(|^\\s*loader\\.lazy|-\\*-"
+    }],
     // Maximum depth callbacks can be nested.
     "max-nested-callbacks": [2, 3],
     // Don't limit the number of parameters that can be used in a function.
@@ -321,7 +326,8 @@
     // Disallow unreachable statements after a return, throw, continue, or break
     // statement.
     "no-unreachable": 2,
-    // Disallow global and local variables that aren't used, but allow unused function arguments.
+    // Disallow global and local variables that aren't used, but allow unused
+    // function arguments.
     "no-unused-vars": [2, {"vars": "all", "args": "none"}],
     // Allow using variables before they are defined.
     "no-use-before-define": 0,
@@ -464,4 +470,4 @@
     // enforce operators to be placed before or after line breaks
     "operator-linebreak": 0,
   }
-}
+};
diff --git a/devtools/.eslintrc.mochitests b/devtools/.eslintrc.mochitests.js
similarity index 85%
rename from devtools/.eslintrc.mochitests
rename to devtools/.eslintrc.mochitests.js
index 8a3f9b6ad871..6805c2000f98 100644
--- a/devtools/.eslintrc.mochitests
+++ b/devtools/.eslintrc.mochitests.js
@@ -1,7 +1,7 @@
 // Parent config file for all devtools browser mochitest files.
-{
+module.exports = {
   "extends": [
-    "../testing/mochitest/browser.eslintrc"
+    "../testing/mochitest/browser.eslintrc.js"
   ],
   // All globals made available in the test environment.
   "globals": {
@@ -17,4 +17,4 @@
     // Tests can always import anything.
     "mozilla/reject-some-requires": 0,
   },
-}
+};
diff --git a/devtools/.eslintrc.xpcshell b/devtools/.eslintrc.xpcshell.js
similarity index 91%
rename from devtools/.eslintrc.xpcshell
rename to devtools/.eslintrc.xpcshell.js
index fc6594d3ef4e..4c8bdfa78e6d 100644
--- a/devtools/.eslintrc.xpcshell
+++ b/devtools/.eslintrc.xpcshell.js
@@ -1,7 +1,7 @@
 // Parent config file for all devtools xpcshell files.
-{
+module.exports = {
   "extends": [
-    "../testing/xpcshell/xpcshell.eslintrc"
+    "../testing/xpcshell/xpcshell.eslintrc.js"
   ],
   "rules": {
     // Allow non-camelcase so that run_test doesn't produce a warning.
@@ -18,4 +18,4 @@
     // Tests can always import anything.
     "mozilla/reject-some-requires": 0,
   }
-}
+};
diff --git a/devtools/client/aboutdebugging/test/.eslintrc b/devtools/client/aboutdebugging/test/.eslintrc.js
similarity index 88%
rename from devtools/client/aboutdebugging/test/.eslintrc
rename to devtools/client/aboutdebugging/test/.eslintrc.js
index 75fa04828751..8c4bee0ef57a 100644
--- a/devtools/client/aboutdebugging/test/.eslintrc
+++ b/devtools/client/aboutdebugging/test/.eslintrc.js
@@ -1,6 +1,8 @@
-{
+"use strict";
+
+module.exports = {
   // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests",
+  "extends": "../../../.eslintrc.mochitests.js",
   // All globals made available in aboutdebugging head.js file.
   "globals": {
     "AddonManager": true,
@@ -21,4 +23,4 @@
     "waitForMutation": true,
     "waitForServiceWorkerRegistered": true
   }
-}
+};
diff --git a/devtools/client/animationinspector/test/.eslintrc b/devtools/client/animationinspector/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/animationinspector/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/animationinspector/test/.eslintrc.js b/devtools/client/animationinspector/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/animationinspector/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/animationinspector/test/unit/.eslintrc b/devtools/client/animationinspector/test/unit/.eslintrc
deleted file mode 100644
index 3fe48b834e19..000000000000
--- a/devtools/client/animationinspector/test/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
\ No newline at end of file
diff --git a/devtools/client/animationinspector/test/unit/.eslintrc.js b/devtools/client/animationinspector/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..59adf410a6ff
--- /dev/null
+++ b/devtools/client/animationinspector/test/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/client/canvasdebugger/test/.eslintrc b/devtools/client/canvasdebugger/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/canvasdebugger/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/canvasdebugger/test/.eslintrc.js b/devtools/client/canvasdebugger/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/canvasdebugger/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/commandline/test/.eslintrc b/devtools/client/commandline/test/.eslintrc.js
similarity index 59%
rename from devtools/client/commandline/test/.eslintrc
rename to devtools/client/commandline/test/.eslintrc.js
index 7ee9912f0253..815b63a0e7fc 100644
--- a/devtools/client/commandline/test/.eslintrc
+++ b/devtools/client/commandline/test/.eslintrc.js
@@ -1,8 +1,10 @@
-{
+"use strict";
+
+module.exports = {
   // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests",
+  "extends": "../../../.eslintrc.mochitests.js",
   "globals": {
     "helpers": true,
     "assert": true
   }
-}
+};
diff --git a/devtools/client/debugger/new/test/mochitest/.eslintrc b/devtools/client/debugger/new/test/mochitest/.eslintrc.js
similarity index 98%
rename from devtools/client/debugger/new/test/mochitest/.eslintrc
rename to devtools/client/debugger/new/test/mochitest/.eslintrc.js
index df67615c68a6..8c095c350dc0 100644
--- a/devtools/client/debugger/new/test/mochitest/.eslintrc
+++ b/devtools/client/debugger/new/test/mochitest/.eslintrc.js
@@ -1,4 +1,6 @@
-{
+"use strict";
+
+module.exports = {
   "globals": {
     "add_task": false,
     "Assert": false,
@@ -70,4 +72,4 @@
     "pressKey": false,
     "EXAMPLE_URL": false
   }
-}
+};
diff --git a/devtools/client/debugger/test/.eslintrc b/devtools/client/debugger/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/debugger/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/debugger/test/.eslintrc.js b/devtools/client/debugger/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/debugger/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/dom/.eslintrc b/devtools/client/dom/.eslintrc.js
similarity index 87%
rename from devtools/client/dom/.eslintrc
rename to devtools/client/dom/.eslintrc.js
index cdef8a49e00a..136011e4eff7 100644
--- a/devtools/client/dom/.eslintrc
+++ b/devtools/client/dom/.eslintrc.js
@@ -1,4 +1,6 @@
-{
+"use strict";
+
+module.exports = {
   "globals": {
     "XMLHttpRequest": true,
     "window": true,
@@ -12,4 +14,4 @@
     "indent": 0,
     "padded-blocks": 0,
   }
-}
+};
diff --git a/devtools/client/dom/test/.eslintrc b/devtools/client/dom/test/.eslintrc
deleted file mode 100644
index b59c5f09df63..000000000000
--- a/devtools/client/dom/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests",
-}
diff --git a/devtools/client/dom/test/.eslintrc.js b/devtools/client/dom/test/.eslintrc.js
new file mode 100644
index 000000000000..14098553359f
--- /dev/null
+++ b/devtools/client/dom/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js",
+};
diff --git a/devtools/client/framework/test/.eslintrc b/devtools/client/framework/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/framework/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/framework/test/.eslintrc.js b/devtools/client/framework/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/framework/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/inspector/.eslintrc b/devtools/client/inspector/.eslintrc.js
similarity index 81%
rename from devtools/client/inspector/.eslintrc
rename to devtools/client/inspector/.eslintrc.js
index cb0a3d43c1ca..635ebd05e97e 100644
--- a/devtools/client/inspector/.eslintrc
+++ b/devtools/client/inspector/.eslintrc.js
@@ -1,12 +1,15 @@
-{
+"use strict";
+
+module.exports = {
   // Extend from the devtools eslintrc.
-  "extends": "../../.eslintrc",
+  "extends": "../../.eslintrc.js",
 
   "rules": {
     // The inspector is being migrated to HTML and cleaned of
     // chrome-privileged code, so this rule disallows requiring chrome
     // code. Some files in the inspector disable this rule still. The
     // goal is to enable the rule globally on all files.
+    /* eslint-disable max-len */
     "mozilla/reject-some-requires": [2, "^(chrome|chrome:.*|resource:.*|devtools/server/.*|.*\\.jsm|devtools/shared/platform/(chome|content)/.*)$"],
   },
-}
+};
diff --git a/devtools/client/inspector/components/test/.eslintrc b/devtools/client/inspector/components/test/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/inspector/components/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/inspector/components/test/.eslintrc.js b/devtools/client/inspector/components/test/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/inspector/components/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/inspector/computed/test/.eslintrc b/devtools/client/inspector/computed/test/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/inspector/computed/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/inspector/computed/test/.eslintrc.js b/devtools/client/inspector/computed/test/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/inspector/computed/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/inspector/fonts/test/.eslintrc b/devtools/client/inspector/fonts/test/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/inspector/fonts/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/inspector/fonts/test/.eslintrc.js b/devtools/client/inspector/fonts/test/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/inspector/fonts/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/inspector/markup/test/.eslintrc b/devtools/client/inspector/markup/test/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/inspector/markup/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/inspector/markup/test/.eslintrc.js b/devtools/client/inspector/markup/test/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/inspector/markup/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/inspector/rules/test/.eslintrc b/devtools/client/inspector/rules/test/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/inspector/rules/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/inspector/rules/test/.eslintrc.js b/devtools/client/inspector/rules/test/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/inspector/rules/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/inspector/shared/test/.eslintrc b/devtools/client/inspector/shared/test/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/inspector/shared/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/inspector/shared/test/.eslintrc.js b/devtools/client/inspector/shared/test/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/inspector/shared/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/inspector/test/.eslintrc b/devtools/client/inspector/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/inspector/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/inspector/test/.eslintrc.js b/devtools/client/inspector/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/inspector/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/jsonview/.eslintrc b/devtools/client/jsonview/.eslintrc.js
similarity index 77%
rename from devtools/client/jsonview/.eslintrc
rename to devtools/client/jsonview/.eslintrc.js
index 34c7a4140b3c..bd1e319818c9 100644
--- a/devtools/client/jsonview/.eslintrc
+++ b/devtools/client/jsonview/.eslintrc.js
@@ -1,4 +1,6 @@
-{
+"use strict";
+
+module.exports = {
   "globals": {
     "define": true,
     "document": true,
@@ -6,4 +8,4 @@
     "CustomEvent": true,
     "Locale": true
   }
-}
+};
diff --git a/devtools/client/jsonview/test/.eslintrc b/devtools/client/jsonview/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/jsonview/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/jsonview/test/.eslintrc.js b/devtools/client/jsonview/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/jsonview/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/memory/test/browser/.eslintrc b/devtools/client/memory/test/browser/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/memory/test/browser/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/memory/test/browser/.eslintrc.js b/devtools/client/memory/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/memory/test/browser/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/memory/test/unit/.eslintrc b/devtools/client/memory/test/unit/.eslintrc
deleted file mode 100644
index 3a133a92001f..000000000000
--- a/devtools/client/memory/test/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
diff --git a/devtools/client/memory/test/unit/.eslintrc.js b/devtools/client/memory/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..aec096a0fc7d
--- /dev/null
+++ b/devtools/client/memory/test/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/client/netmonitor/.eslintrc b/devtools/client/netmonitor/.eslintrc.js
similarity index 81%
rename from devtools/client/netmonitor/.eslintrc
rename to devtools/client/netmonitor/.eslintrc.js
index 4d83601e14ed..a7ab1fdfa719 100644
--- a/devtools/client/netmonitor/.eslintrc
+++ b/devtools/client/netmonitor/.eslintrc.js
@@ -1,12 +1,15 @@
-{
+"use strict";
+
+module.exports = {
   // Extend from the devtools eslintrc.
-  "extends": "../../.eslintrc",
+  "extends": "../../.eslintrc.js",
 
   "rules": {
     // The netmonitor is being migrated to HTML and cleaned of
     // chrome-privileged code, so this rule disallows requiring chrome
     // code. Some files in the netmonitor disable this rule still. The
     // goal is to enable the rule globally on all files.
+    /* eslint-disable max-len */
     "mozilla/reject-some-requires": [2, "^(chrome|chrome:.*|resource:.*|devtools/server/.*|.*\\.jsm|devtools/shared/platform/(chome|content)/.*)$"],
   },
-}
+};
diff --git a/devtools/client/netmonitor/har/test/.eslintrc b/devtools/client/netmonitor/har/test/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/netmonitor/har/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/netmonitor/har/test/.eslintrc.js b/devtools/client/netmonitor/har/test/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/netmonitor/har/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/netmonitor/test/.eslintrc b/devtools/client/netmonitor/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/netmonitor/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/netmonitor/test/.eslintrc.js b/devtools/client/netmonitor/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/netmonitor/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/performance/test/.eslintrc b/devtools/client/performance/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/performance/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/performance/test/.eslintrc.js b/devtools/client/performance/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/performance/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/performance/test/unit/.eslintrc b/devtools/client/performance/test/unit/.eslintrc
deleted file mode 100644
index 3a133a92001f..000000000000
--- a/devtools/client/performance/test/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
diff --git a/devtools/client/performance/test/unit/.eslintrc.js b/devtools/client/performance/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..aec096a0fc7d
--- /dev/null
+++ b/devtools/client/performance/test/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/client/projecteditor/test/.eslintrc b/devtools/client/projecteditor/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/projecteditor/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/projecteditor/test/.eslintrc.js b/devtools/client/projecteditor/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/projecteditor/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/promisedebugger/test/.eslintrc b/devtools/client/promisedebugger/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/promisedebugger/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/promisedebugger/test/.eslintrc.js b/devtools/client/promisedebugger/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/promisedebugger/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/responsive.html/test/browser/.eslintrc b/devtools/client/responsive.html/test/browser/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/responsive.html/test/browser/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/responsive.html/test/browser/.eslintrc.js b/devtools/client/responsive.html/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/responsive.html/test/browser/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/responsive.html/test/unit/.eslintrc b/devtools/client/responsive.html/test/unit/.eslintrc
deleted file mode 100644
index 914416e95772..000000000000
--- a/devtools/client/responsive.html/test/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for xpcshell.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
diff --git a/devtools/client/responsive.html/test/unit/.eslintrc.js b/devtools/client/responsive.html/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..f879b967bd46
--- /dev/null
+++ b/devtools/client/responsive.html/test/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for xpcshell.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/client/responsivedesign/test/.eslintrc b/devtools/client/responsivedesign/test/.eslintrc.js
similarity index 60%
rename from devtools/client/responsivedesign/test/.eslintrc
rename to devtools/client/responsivedesign/test/.eslintrc.js
index 35f62c76be80..ba1263286d9b 100644
--- a/devtools/client/responsivedesign/test/.eslintrc
+++ b/devtools/client/responsivedesign/test/.eslintrc.js
@@ -1,8 +1,10 @@
-{
+"use strict";
+
+module.exports = {
   // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests",
+  "extends": "../../../.eslintrc.mochitests.js",
   "globals": {
     "ResponsiveUI": true,
     "helpers": true
   }
-}
+};
diff --git a/devtools/client/scratchpad/test/.eslintrc b/devtools/client/scratchpad/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/scratchpad/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/scratchpad/test/.eslintrc.js b/devtools/client/scratchpad/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/scratchpad/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/shadereditor/test/.eslintrc b/devtools/client/shadereditor/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/shadereditor/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/shadereditor/test/.eslintrc.js b/devtools/client/shadereditor/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/shadereditor/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/shared/components/.eslintrc b/devtools/client/shared/components/.eslintrc.js
similarity index 51%
rename from devtools/client/shared/components/.eslintrc
rename to devtools/client/shared/components/.eslintrc.js
index 493eb7158886..3112895e9354 100644
--- a/devtools/client/shared/components/.eslintrc
+++ b/devtools/client/shared/components/.eslintrc.js
@@ -1,5 +1,7 @@
-{
+"use strict";
+
+module.exports = {
   "globals": {
     "define": true,
   }
-}
+};
diff --git a/devtools/client/shared/components/test/browser/.eslintrc b/devtools/client/shared/components/test/browser/.eslintrc
deleted file mode 100644
index 7f990f3fb45f..000000000000
--- a/devtools/client/shared/components/test/browser/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../../.eslintrc.mochitests",
-}
diff --git a/devtools/client/shared/components/test/browser/.eslintrc.js b/devtools/client/shared/components/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..76904829d549
--- /dev/null
+++ b/devtools/client/shared/components/test/browser/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../../.eslintrc.mochitests.js",
+};
diff --git a/devtools/client/shared/components/test/mochitest/.eslintrc b/devtools/client/shared/components/test/mochitest/.eslintrc
deleted file mode 100644
index d03a34bff0bc..000000000000
--- a/devtools/client/shared/components/test/mochitest/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/shared/components/test/mochitest/.eslintrc.js b/devtools/client/shared/components/test/mochitest/.eslintrc.js
new file mode 100644
index 000000000000..677cbb4243df
--- /dev/null
+++ b/devtools/client/shared/components/test/mochitest/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/shared/shim/test/.eslintrc b/devtools/client/shared/shim/test/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/client/shared/shim/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/shared/shim/test/.eslintrc.js b/devtools/client/shared/shim/test/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/client/shared/shim/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/shared/test/.eslintrc b/devtools/client/shared/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/shared/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/shared/test/.eslintrc.js b/devtools/client/shared/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/shared/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/shared/test/unit/.eslintrc b/devtools/client/shared/test/unit/.eslintrc
deleted file mode 100644
index 3fe48b834e19..000000000000
--- a/devtools/client/shared/test/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
\ No newline at end of file
diff --git a/devtools/client/shared/test/unit/.eslintrc.js b/devtools/client/shared/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..59adf410a6ff
--- /dev/null
+++ b/devtools/client/shared/test/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/client/sourceeditor/.eslintrc b/devtools/client/sourceeditor/.eslintrc.js
similarity index 79%
rename from devtools/client/sourceeditor/.eslintrc
rename to devtools/client/sourceeditor/.eslintrc.js
index 22e9443e7b99..85fd3d842a7a 100644
--- a/devtools/client/sourceeditor/.eslintrc
+++ b/devtools/client/sourceeditor/.eslintrc.js
@@ -1,12 +1,15 @@
-{
+"use strict";
+
+module.exports = {
   // Extend from the devtools eslintrc.
-  "extends": "../../.eslintrc",
+  "extends": "../../.eslintrc.js",
 
   "rules": {
     // The inspector is being migrated to HTML and cleaned of
     // chrome-privileged code, so this rule disallows requiring chrome
     // code. Some files here disable this rule still. The
     // goal is to enable the rule globally on all files.
+    /* eslint-disable max-len */
     "mozilla/reject-some-requires": [2, "^(chrome|chrome:.*|resource:.*|devtools/server/.*|.*\\.jsm)$"],
   },
-}
+};
diff --git a/devtools/client/sourceeditor/test/.eslintrc b/devtools/client/sourceeditor/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/sourceeditor/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/sourceeditor/test/.eslintrc.js b/devtools/client/sourceeditor/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/sourceeditor/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/storage/test/.eslintrc b/devtools/client/storage/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/storage/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/storage/test/.eslintrc.js b/devtools/client/storage/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/storage/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/styleeditor/test/.eslintrc b/devtools/client/styleeditor/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/styleeditor/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/styleeditor/test/.eslintrc.js b/devtools/client/styleeditor/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/styleeditor/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/webaudioeditor/test/.eslintrc b/devtools/client/webaudioeditor/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/webaudioeditor/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/webaudioeditor/test/.eslintrc.js b/devtools/client/webaudioeditor/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/webaudioeditor/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/webconsole/net/.eslintrc b/devtools/client/webconsole/net/.eslintrc.js
similarity index 90%
rename from devtools/client/webconsole/net/.eslintrc
rename to devtools/client/webconsole/net/.eslintrc.js
index 69abb7aebaf2..cbe23f4d6d4d 100644
--- a/devtools/client/webconsole/net/.eslintrc
+++ b/devtools/client/webconsole/net/.eslintrc.js
@@ -1,4 +1,6 @@
-{
+"use strict";
+
+module.exports = {
   "globals": {
     "Locale": true,
     "Document": true,
@@ -15,4 +17,4 @@
   "rules": {
     "no-unused-vars": [2, {"args": "none"}],
   }
-}
+};
diff --git a/devtools/client/webconsole/net/test/mochitest/.eslintrc b/devtools/client/webconsole/net/test/mochitest/.eslintrc
deleted file mode 100644
index 7f990f3fb45f..000000000000
--- a/devtools/client/webconsole/net/test/mochitest/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../../.eslintrc.mochitests",
-}
diff --git a/devtools/client/webconsole/net/test/mochitest/.eslintrc.js b/devtools/client/webconsole/net/test/mochitest/.eslintrc.js
new file mode 100644
index 000000000000..76904829d549
--- /dev/null
+++ b/devtools/client/webconsole/net/test/mochitest/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../../.eslintrc.mochitests.js",
+};
diff --git a/devtools/client/webconsole/net/test/unit/.eslintrc b/devtools/client/webconsole/net/test/unit/.eslintrc
deleted file mode 100644
index 79027b14191c..000000000000
--- a/devtools/client/webconsole/net/test/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../../../.eslintrc.xpcshell"
-}
\ No newline at end of file
diff --git a/devtools/client/webconsole/net/test/unit/.eslintrc.js b/devtools/client/webconsole/net/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..54a9a6361b5c
--- /dev/null
+++ b/devtools/client/webconsole/net/test/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/client/webconsole/new-console-output/test/.eslintrc b/devtools/client/webconsole/new-console-output/test/.eslintrc
deleted file mode 100644
index 4c06df61c516..000000000000
--- a/devtools/client/webconsole/new-console-output/test/.eslintrc
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "extends": ["../../../../.eslintrc.xpcshell"]
-}
diff --git a/devtools/client/webconsole/new-console-output/test/.eslintrc.js b/devtools/client/webconsole/new-console-output/test/.eslintrc.js
new file mode 100644
index 000000000000..e010df386412
--- /dev/null
+++ b/devtools/client/webconsole/new-console-output/test/.eslintrc.js
@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = {
+  "extends": ["../../../../.eslintrc.xpcshell.js"]
+};
diff --git a/devtools/client/webconsole/test/.eslintrc b/devtools/client/webconsole/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/webconsole/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/webconsole/test/.eslintrc.js b/devtools/client/webconsole/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/webconsole/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/client/webide/test/.eslintrc b/devtools/client/webide/test/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/client/webide/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/client/webide/test/.eslintrc.js b/devtools/client/webide/test/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/client/webide/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/server/tests/browser/.eslintrc b/devtools/server/tests/browser/.eslintrc
deleted file mode 100644
index e076b65226e6..000000000000
--- a/devtools/server/tests/browser/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools mochitest eslintrc config.
-  "extends": "../../../.eslintrc.xpcshell"
-}
diff --git a/devtools/server/tests/browser/.eslintrc.js b/devtools/server/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..c5b919ce337f
--- /dev/null
+++ b/devtools/server/tests/browser/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools mochitest eslintrc config.
+  "extends": "../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/server/tests/mochitest/.eslintrc b/devtools/server/tests/mochitest/.eslintrc
deleted file mode 100644
index e076b65226e6..000000000000
--- a/devtools/server/tests/mochitest/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools mochitest eslintrc config.
-  "extends": "../../../.eslintrc.xpcshell"
-}
diff --git a/devtools/server/tests/mochitest/.eslintrc.js b/devtools/server/tests/mochitest/.eslintrc.js
new file mode 100644
index 000000000000..c5b919ce337f
--- /dev/null
+++ b/devtools/server/tests/mochitest/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools mochitest eslintrc config.
+  "extends": "../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/server/tests/unit/.eslintrc b/devtools/server/tests/unit/.eslintrc
deleted file mode 100644
index 11b5c571ef6c..000000000000
--- a/devtools/server/tests/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../.eslintrc.xpcshell"
-}
diff --git a/devtools/server/tests/unit/.eslintrc.js b/devtools/server/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..0124280192b7
--- /dev/null
+++ b/devtools/server/tests/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/shared/heapsnapshot/tests/unit/.eslintrc b/devtools/shared/heapsnapshot/tests/unit/.eslintrc
deleted file mode 100644
index 3fe48b834e19..000000000000
--- a/devtools/shared/heapsnapshot/tests/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
\ No newline at end of file
diff --git a/devtools/shared/heapsnapshot/tests/unit/.eslintrc.js b/devtools/shared/heapsnapshot/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..59adf410a6ff
--- /dev/null
+++ b/devtools/shared/heapsnapshot/tests/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/shared/platform/content/.eslintrc b/devtools/shared/platform/content/.eslintrc.js
similarity index 71%
rename from devtools/shared/platform/content/.eslintrc
rename to devtools/shared/platform/content/.eslintrc.js
index 2e8d7f749f45..caf942873a18 100644
--- a/devtools/shared/platform/content/.eslintrc
+++ b/devtools/shared/platform/content/.eslintrc.js
@@ -1,9 +1,12 @@
-{
+"use strict";
+
+module.exports = {
   // Extend from the devtools eslintrc.
-  "extends": "../../../.eslintrc",
+  "extends": "../../../.eslintrc.js",
 
   "rules": {
+    /* eslint-disable max-len */
     // All code in this directory must be content-clean.
     "mozilla/reject-some-requires": [2, "^(chrome|chrome:.*|resource:.*|devtools/server/.*|.*\\.jsm|devtools/shared/platform/(chome|content)/.*)$"],
   },
-}
+};
diff --git a/devtools/shared/platform/content/test/.eslintrc b/devtools/shared/platform/content/test/.eslintrc
deleted file mode 100644
index 211e047bc776..000000000000
--- a/devtools/shared/platform/content/test/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
diff --git a/devtools/shared/platform/content/test/.eslintrc.js b/devtools/shared/platform/content/test/.eslintrc.js
new file mode 100644
index 000000000000..59adf410a6ff
--- /dev/null
+++ b/devtools/shared/platform/content/test/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/shared/security/tests/unit/.eslintrc b/devtools/shared/security/tests/unit/.eslintrc
deleted file mode 100644
index 3fe48b834e19..000000000000
--- a/devtools/shared/security/tests/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
\ No newline at end of file
diff --git a/devtools/shared/security/tests/unit/.eslintrc.js b/devtools/shared/security/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..59adf410a6ff
--- /dev/null
+++ b/devtools/shared/security/tests/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/shared/tests/browser/.eslintrc b/devtools/shared/tests/browser/.eslintrc
deleted file mode 100644
index 044c3e4f49e8..000000000000
--- a/devtools/shared/tests/browser/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../.eslintrc.mochitests"
-}
diff --git a/devtools/shared/tests/browser/.eslintrc.js b/devtools/shared/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..8d15a76d9b8c
--- /dev/null
+++ b/devtools/shared/tests/browser/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/shared/tests/unit/.eslintrc b/devtools/shared/tests/unit/.eslintrc
deleted file mode 100644
index 11b5c571ef6c..000000000000
--- a/devtools/shared/tests/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../.eslintrc.xpcshell"
-}
diff --git a/devtools/shared/tests/unit/.eslintrc.js b/devtools/shared/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..0124280192b7
--- /dev/null
+++ b/devtools/shared/tests/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/shared/transport/tests/unit/.eslintrc b/devtools/shared/transport/tests/unit/.eslintrc
deleted file mode 100644
index 3fe48b834e19..000000000000
--- a/devtools/shared/transport/tests/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
\ No newline at end of file
diff --git a/devtools/shared/transport/tests/unit/.eslintrc.js b/devtools/shared/transport/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..59adf410a6ff
--- /dev/null
+++ b/devtools/shared/transport/tests/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/shared/webconsole/test/unit/.eslintrc b/devtools/shared/webconsole/test/unit/.eslintrc
deleted file mode 100644
index 3fe48b834e19..000000000000
--- a/devtools/shared/webconsole/test/unit/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the common devtools xpcshell eslintrc config.
-  "extends": "../../../../.eslintrc.xpcshell"
-}
\ No newline at end of file
diff --git a/devtools/shared/webconsole/test/unit/.eslintrc.js b/devtools/shared/webconsole/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..59adf410a6ff
--- /dev/null
+++ b/devtools/shared/webconsole/test/unit/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the common devtools xpcshell eslintrc config.
+  "extends": "../../../../.eslintrc.xpcshell.js"
+};
diff --git a/devtools/shared/worker/tests/browser/.eslintrc b/devtools/shared/worker/tests/browser/.eslintrc
deleted file mode 100644
index c73d0b308f27..000000000000
--- a/devtools/shared/worker/tests/browser/.eslintrc
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  // Extend from the shared list of defined globals for mochitests.
-  "extends": "../../../../.eslintrc.mochitests"
-}
diff --git a/devtools/shared/worker/tests/browser/.eslintrc.js b/devtools/shared/worker/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..698ae9181a0a
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/mobile/android/components/extensions/.eslintrc b/mobile/android/components/extensions/.eslintrc.js
similarity index 59%
rename from mobile/android/components/extensions/.eslintrc
rename to mobile/android/components/extensions/.eslintrc.js
index b4e52caf7080..4b67e27b883d 100644
--- a/mobile/android/components/extensions/.eslintrc
+++ b/mobile/android/components/extensions/.eslintrc.js
@@ -1,3 +1,5 @@
-{
-  "extends": "../../../../toolkit/components/extensions/.eslintrc",
-}
+"use strict";
+
+module.exports = {
+  "extends": "../../../../toolkit/components/extensions/.eslintrc.js",
+};
diff --git a/mobile/android/components/extensions/test/mochitest/.eslintrc b/mobile/android/components/extensions/test/mochitest/.eslintrc.js
similarity index 69%
rename from mobile/android/components/extensions/test/mochitest/.eslintrc
rename to mobile/android/components/extensions/test/mochitest/.eslintrc.js
index 9048c650e2b2..5f9059e18e5d 100644
--- a/mobile/android/components/extensions/test/mochitest/.eslintrc
+++ b/mobile/android/components/extensions/test/mochitest/.eslintrc.js
@@ -1,8 +1,10 @@
-{
-  "extends": "../../../../../../toolkit/components/extensions/test/mochitest/.eslintrc",
+"use strict";
+
+module.exports = {
+  "extends": "../../../../../../toolkit/components/extensions/test/mochitest/.eslintrc.js",
 
   "globals": {
     "isPageActionShown": true,
     "clickPageAction": true,
   },
-}
+};
diff --git a/security/manager/.eslintrc.json b/security/manager/.eslintrc.js
similarity index 98%
rename from security/manager/.eslintrc.json
rename to security/manager/.eslintrc.js
index 64dd80bd21ba..3005430ddf1c 100644
--- a/security/manager/.eslintrc.json
+++ b/security/manager/.eslintrc.js
@@ -1,4 +1,6 @@
-{
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
   "rules": {
     // Braces only needed for multi-line arrow function blocks
     "arrow-body-style": [2, "as-needed"],
@@ -218,4 +220,4 @@
     "Components": false,
     "dump": false
   }
-}
+};
diff --git a/security/manager/ssl/tests/.eslintrc.json b/security/manager/ssl/tests/.eslintrc.js
similarity index 60%
rename from security/manager/ssl/tests/.eslintrc.json
rename to security/manager/ssl/tests/.eslintrc.js
index b92a3775646d..e686a6c39cd7 100644
--- a/security/manager/ssl/tests/.eslintrc.json
+++ b/security/manager/ssl/tests/.eslintrc.js
@@ -1,6 +1,8 @@
-{
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
   "rules": {
     // Disallow non-top level |var| declarations.
     "mozilla/var-only-at-top-level": 2
   }
-}
+};
diff --git a/security/manager/ssl/tests/mochitest/browser/.eslintrc.js b/security/manager/ssl/tests/mochitest/browser/.eslintrc.js
new file mode 100644
index 000000000000..c15988365efc
--- /dev/null
+++ b/security/manager/ssl/tests/mochitest/browser/.eslintrc.js
@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../../../../../testing/mochitest/browser.eslintrc.js"
+};
diff --git a/security/manager/ssl/tests/mochitest/browser/.eslintrc.json b/security/manager/ssl/tests/mochitest/browser/.eslintrc.json
deleted file mode 100644
index ddbc4496bc66..000000000000
--- a/security/manager/ssl/tests/mochitest/browser/.eslintrc.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "extends": "../../../../../../testing/mochitest/browser.eslintrc"
-}
diff --git a/security/manager/ssl/tests/mochitest/mixedcontent/.eslintrc.js b/security/manager/ssl/tests/mochitest/mixedcontent/.eslintrc.js
new file mode 100644
index 000000000000..d61bb2044f22
--- /dev/null
+++ b/security/manager/ssl/tests/mochitest/mixedcontent/.eslintrc.js
@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../../../../../testing/mochitest/mochitest.eslintrc.js"
+};
diff --git a/security/manager/ssl/tests/mochitest/mixedcontent/.eslintrc.json b/security/manager/ssl/tests/mochitest/mixedcontent/.eslintrc.json
deleted file mode 100644
index ef319ec3e080..000000000000
--- a/security/manager/ssl/tests/mochitest/mixedcontent/.eslintrc.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "extends": "../../../../../../testing/mochitest/mochitest.eslintrc"
-}
diff --git a/security/manager/ssl/tests/mochitest/stricttransportsecurity/.eslintrc.json b/security/manager/ssl/tests/mochitest/stricttransportsecurity/.eslintrc.js
similarity index 80%
rename from security/manager/ssl/tests/mochitest/stricttransportsecurity/.eslintrc.json
rename to security/manager/ssl/tests/mochitest/stricttransportsecurity/.eslintrc.js
index afbebc284ca1..74b7a1a07105 100644
--- a/security/manager/ssl/tests/mochitest/stricttransportsecurity/.eslintrc.json
+++ b/security/manager/ssl/tests/mochitest/stricttransportsecurity/.eslintrc.js
@@ -1,7 +1,9 @@
-{
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
   // mochitest-chrome tests also exist in this directory, but don't appear to
   // use anything not also available to plain mochitests. Since plain mochitests
   // are the majority, we take the safer option and only extend the
   // mochitest-plain eslintrc file.
-  "extends": "../../../../../../testing/mochitest/mochitest.eslintrc"
-}
+  "extends": "../../../../../../testing/mochitest/mochitest.eslintrc.js"
+};
diff --git a/security/manager/ssl/tests/unit/.eslintrc.js b/security/manager/ssl/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..1f96e78215a7
--- /dev/null
+++ b/security/manager/ssl/tests/unit/.eslintrc.js
@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+};
diff --git a/security/manager/ssl/tests/unit/.eslintrc.json b/security/manager/ssl/tests/unit/.eslintrc.json
deleted file mode 100644
index 8b5c3a28039e..000000000000
--- a/security/manager/ssl/tests/unit/.eslintrc.json
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "extends": "../../../../../testing/xpcshell/xpcshell.eslintrc"
-}
diff --git a/security/manager/tools/.eslintrc.json b/security/manager/tools/.eslintrc.js
similarity index 69%
rename from security/manager/tools/.eslintrc.json
rename to security/manager/tools/.eslintrc.js
index 0fd26937dfc3..49de9eadd141 100644
--- a/security/manager/tools/.eslintrc.json
+++ b/security/manager/tools/.eslintrc.js
@@ -1,7 +1,9 @@
-{
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
   "globals": {
     // JS files in this folder are commonly xpcshell scripts where |arguments|
     // is defined in the global scope.
     "arguments": false
   }
-}
+};
diff --git a/storage/.eslintrc b/storage/.eslintrc
deleted file mode 100644
index e7e9d8ce5928..000000000000
--- a/storage/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../toolkit/.eslintrc"
-  ]
-}
diff --git a/storage/.eslintrc.js b/storage/.eslintrc.js
new file mode 100644
index 000000000000..69afc2f3cb68
--- /dev/null
+++ b/storage/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../toolkit/.eslintrc.js"
+  ]
+};
diff --git a/testing/mochitest/browser.eslintrc b/testing/mochitest/browser.eslintrc.js
similarity index 96%
rename from testing/mochitest/browser.eslintrc
rename to testing/mochitest/browser.eslintrc.js
index 0e1100d4dd24..80fe312b5bc6 100644
--- a/testing/mochitest/browser.eslintrc
+++ b/testing/mochitest/browser.eslintrc.js
@@ -1,5 +1,5 @@
 // Parent config file for all browser-chrome files.
-{
+module.exports = {
   "rules": {
     "mozilla/import-headjs-globals": 2,
     "mozilla/import-browserjs-globals": 2,
@@ -7,6 +7,7 @@
 
   "env": {
     "browser": true,
+    //"node": true
   },
 
   // All globals made available in the test environment.
@@ -44,4 +45,4 @@
     "waitForExplicitFinish": false,
     "waitForFocus": false,
   }
-}
+};
diff --git a/testing/mochitest/chrome.eslintrc b/testing/mochitest/chrome.eslintrc.js
similarity index 97%
rename from testing/mochitest/chrome.eslintrc
rename to testing/mochitest/chrome.eslintrc.js
index 5a56d84195a0..c38d44b91bc7 100644
--- a/testing/mochitest/chrome.eslintrc
+++ b/testing/mochitest/chrome.eslintrc.js
@@ -1,5 +1,5 @@
 // Parent config file for all mochitest files.
-{
+module.exports = {
   rules: {
     "mozilla/import-headjs-globals": 1,
   },
@@ -35,4 +35,4 @@
     "waitForExplicitFinish": false,
     "waitForFocus": false,
   }
-}
+};
diff --git a/testing/mochitest/mochitest.eslintrc b/testing/mochitest/mochitest.eslintrc.js
similarity index 97%
rename from testing/mochitest/mochitest.eslintrc
rename to testing/mochitest/mochitest.eslintrc.js
index 33f0790acb79..27749fe4a52b 100644
--- a/testing/mochitest/mochitest.eslintrc
+++ b/testing/mochitest/mochitest.eslintrc.js
@@ -1,5 +1,5 @@
 // Parent config file for all mochitest files.
-{
+module.exports = {
   rules: {
     "mozilla/import-headjs-globals": 1,
   },
@@ -36,4 +36,4 @@
     "waitForExplicitFinish": false,
     "waitForFocus": false,
   }
-}
+};
diff --git a/testing/xpcshell/xpcshell.eslintrc b/testing/xpcshell/xpcshell.eslintrc.js
similarity index 98%
rename from testing/xpcshell/xpcshell.eslintrc
rename to testing/xpcshell/xpcshell.eslintrc.js
index 3648f36d61a5..c6e503785e98 100644
--- a/testing/xpcshell/xpcshell.eslintrc
+++ b/testing/xpcshell/xpcshell.eslintrc.js
@@ -1,5 +1,5 @@
 // Parent config file for all xpcshell files.
-{
+module.exports = {
   rules: {
     "mozilla/import-headjs-globals": 1,
   },
@@ -49,4 +49,4 @@
     "todo_check_false": false,
     "todo_check_true": false,
   }
-}
+};
diff --git a/toolkit/.eslintrc b/toolkit/.eslintrc.js
similarity index 98%
rename from toolkit/.eslintrc
rename to toolkit/.eslintrc.js
index bf58a051619b..9bd917440e0c 100644
--- a/toolkit/.eslintrc
+++ b/toolkit/.eslintrc.js
@@ -1,4 +1,6 @@
-{
+"use strict";
+
+module.exports = {
   // When adding items to this file please check for effects on all of toolkit
   // and browser
   "rules": {
@@ -71,7 +73,7 @@
     "no-else-return": 2,
 
     // No empty statements
-    "no-empty": [2, "allowEmptyCatch": true],
+    "no-empty": [2, {"allowEmptyCatch": true}],
 
     // No empty character classes in regex
     "no-empty-character-class": 2,
@@ -197,4 +199,4 @@
     "openDialog": false,
     "sizeToContent": false,
   }
-}
+};
diff --git a/toolkit/components/aboutmemory/tests/.eslintrc b/toolkit/components/aboutmemory/tests/.eslintrc
deleted file mode 100644
index e2b648435bb8..000000000000
--- a/toolkit/components/aboutmemory/tests/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/components/aboutmemory/tests/.eslintrc.js b/toolkit/components/aboutmemory/tests/.eslintrc.js
new file mode 100644
index 000000000000..2c669d844eb0
--- /dev/null
+++ b/toolkit/components/aboutmemory/tests/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/aboutperformance/tests/browser/.eslintrc b/toolkit/components/aboutperformance/tests/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/aboutperformance/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/aboutperformance/tests/browser/.eslintrc.js b/toolkit/components/aboutperformance/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/aboutperformance/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/addoncompat/tests/browser/.eslintrc b/toolkit/components/addoncompat/tests/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/addoncompat/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/addoncompat/tests/browser/.eslintrc.js b/toolkit/components/addoncompat/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/addoncompat/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/alerts/test/.eslintrc b/toolkit/components/alerts/test/.eslintrc
deleted file mode 100644
index 9174183fccce..000000000000
--- a/toolkit/components/alerts/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/toolkit/components/alerts/test/.eslintrc.js b/toolkit/components/alerts/test/.eslintrc.js
new file mode 100644
index 000000000000..3c788d6d681c
--- /dev/null
+++ b/toolkit/components/alerts/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/asyncshutdown/tests/xpcshell/.eslintrc b/toolkit/components/asyncshutdown/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/asyncshutdown/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/asyncshutdown/tests/xpcshell/.eslintrc.js b/toolkit/components/asyncshutdown/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/asyncshutdown/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/autocomplete/tests/unit/.eslintrc b/toolkit/components/autocomplete/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/autocomplete/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/autocomplete/tests/unit/.eslintrc.js b/toolkit/components/autocomplete/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/autocomplete/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/captivedetect/test/unit/.eslintrc b/toolkit/components/captivedetect/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/captivedetect/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/captivedetect/test/unit/.eslintrc.js b/toolkit/components/captivedetect/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/captivedetect/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/commandlines/test/unit/.eslintrc b/toolkit/components/commandlines/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/commandlines/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/commandlines/test/unit/.eslintrc.js b/toolkit/components/commandlines/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/commandlines/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/commandlines/test/unit_unix/.eslintrc b/toolkit/components/commandlines/test/unit_unix/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/commandlines/test/unit_unix/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/commandlines/test/unit_unix/.eslintrc.js b/toolkit/components/commandlines/test/unit_unix/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/commandlines/test/unit_unix/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/commandlines/test/unit_win/.eslintrc b/toolkit/components/commandlines/test/unit_win/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/commandlines/test/unit_win/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/commandlines/test/unit_win/.eslintrc.js b/toolkit/components/commandlines/test/unit_win/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/commandlines/test/unit_win/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/contentprefs/tests/mochitest/.eslintrc b/toolkit/components/contentprefs/tests/mochitest/.eslintrc
deleted file mode 100644
index 81ae1b0f9207..000000000000
--- a/toolkit/components/contentprefs/tests/mochitest/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/toolkit/components/contentprefs/tests/mochitest/.eslintrc.js b/toolkit/components/contentprefs/tests/mochitest/.eslintrc.js
new file mode 100644
index 000000000000..64a4eda73171
--- /dev/null
+++ b/toolkit/components/contentprefs/tests/mochitest/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/contentprefs/tests/unit/.eslintrc b/toolkit/components/contentprefs/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/contentprefs/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/contentprefs/tests/unit/.eslintrc.js b/toolkit/components/contentprefs/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/contentprefs/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/contentprefs/tests/unit_cps2/.eslintrc b/toolkit/components/contentprefs/tests/unit_cps2/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/contentprefs/tests/unit_cps2/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/contentprefs/tests/unit_cps2/.eslintrc.js b/toolkit/components/contentprefs/tests/unit_cps2/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/contentprefs/tests/unit_cps2/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/crashes/tests/xpcshell/.eslintrc b/toolkit/components/crashes/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/crashes/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/crashes/tests/xpcshell/.eslintrc.js b/toolkit/components/crashes/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/crashes/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/crashmonitor/test/unit/.eslintrc b/toolkit/components/crashmonitor/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/crashmonitor/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/crashmonitor/test/unit/.eslintrc.js b/toolkit/components/crashmonitor/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/crashmonitor/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/ctypes/tests/chrome/.eslintrc b/toolkit/components/ctypes/tests/chrome/.eslintrc
deleted file mode 100644
index 218d988742d2..000000000000
--- a/toolkit/components/ctypes/tests/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/components/ctypes/tests/chrome/.eslintrc.js b/toolkit/components/ctypes/tests/chrome/.eslintrc.js
new file mode 100644
index 000000000000..8c0f4f574c28
--- /dev/null
+++ b/toolkit/components/ctypes/tests/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/ctypes/tests/unit/.eslintrc b/toolkit/components/ctypes/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/ctypes/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/ctypes/tests/unit/.eslintrc.js b/toolkit/components/ctypes/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/ctypes/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/downloads/test/unit/.eslintrc b/toolkit/components/downloads/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/downloads/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/downloads/test/unit/.eslintrc.js b/toolkit/components/downloads/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/downloads/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/extensions/.eslintrc b/toolkit/components/extensions/.eslintrc.js
similarity index 98%
rename from toolkit/components/extensions/.eslintrc
rename to toolkit/components/extensions/.eslintrc.js
index 936688a887a0..225242382894 100644
--- a/toolkit/components/extensions/.eslintrc
+++ b/toolkit/components/extensions/.eslintrc.js
@@ -1,5 +1,7 @@
-{
-  "extends": "../../.eslintrc",
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../.eslintrc.js",
 
   "globals": {
     "Cc": true,
@@ -352,7 +354,7 @@
     "no-inline-comments": 0,
 
     // Disallow use of labels for anything other then loops and switches.
-    "no-labels": [2, { "allowLoop": true }],
+    "no-labels": [2, {"allowLoop": true}],
 
     // Disallow use of multiline strings (use template strings instead).
     "no-multi-str": 1,
@@ -488,5 +490,5 @@
 
     // Disallow creating new instances of String, Number, and Boolean
     "no-new-wrappers": 2,
-  }
-}
+  },
+};
diff --git a/toolkit/components/extensions/test/mochitest/.eslintrc b/toolkit/components/extensions/test/mochitest/.eslintrc.js
similarity index 79%
rename from toolkit/components/extensions/test/mochitest/.eslintrc
rename to toolkit/components/extensions/test/mochitest/.eslintrc.js
index 47e982ecbd37..3a8cd46bcf61 100644
--- a/toolkit/components/extensions/test/mochitest/.eslintrc
+++ b/toolkit/components/extensions/test/mochitest/.eslintrc.js
@@ -1,5 +1,7 @@
-{
-  "extends": "../../../../../testing/mochitest/mochitest.eslintrc",
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../../../../testing/mochitest/mochitest.eslintrc.js",
 
   "env": {
     "webextensions": true,
@@ -15,4 +17,4 @@
     "NetUtil": true,
     "XPCOMUtils": true,
   },
-}
+};
diff --git a/toolkit/components/extensions/test/xpcshell/.eslintrc b/toolkit/components/extensions/test/xpcshell/.eslintrc
deleted file mode 100644
index 03381914eed7..000000000000
--- a/toolkit/components/extensions/test/xpcshell/.eslintrc
+++ /dev/null
@@ -1,7 +0,0 @@
-{
-  "extends": "../../../../../testing/xpcshell/xpcshell.eslintrc",
-
-  "globals": {
-    "browser": false,
-  },
-}
diff --git a/toolkit/components/extensions/test/xpcshell/.eslintrc.js b/toolkit/components/extensions/test/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..3758537ef4df
--- /dev/null
+++ b/toolkit/components/extensions/test/xpcshell/.eslintrc.js
@@ -0,0 +1,9 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../../../../testing/xpcshell/xpcshell.eslintrc.js",
+
+  "globals": {
+    "browser": false,
+  },
+};
diff --git a/toolkit/components/feeds/test/.eslintrc b/toolkit/components/feeds/test/.eslintrc
deleted file mode 100644
index 89368781d3d5..000000000000
--- a/toolkit/components/feeds/test/.eslintrc
+++ /dev/null
@@ -1,6 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/chrome.eslintrc",
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/feeds/test/.eslintrc.js b/toolkit/components/feeds/test/.eslintrc.js
new file mode 100644
index 000000000000..89764b5510e5
--- /dev/null
+++ b/toolkit/components/feeds/test/.eslintrc.js
@@ -0,0 +1,8 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/chrome.eslintrc.js",
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/filepicker/test/unit/.eslintrc b/toolkit/components/filepicker/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/filepicker/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/filepicker/test/unit/.eslintrc.js b/toolkit/components/filepicker/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/filepicker/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/filewatcher/tests/xpcshell/.eslintrc b/toolkit/components/filewatcher/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/filewatcher/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/filewatcher/tests/xpcshell/.eslintrc.js b/toolkit/components/filewatcher/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/filewatcher/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/formautofill/test/browser/.eslintrc b/toolkit/components/formautofill/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/formautofill/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/formautofill/test/browser/.eslintrc.js b/toolkit/components/formautofill/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/formautofill/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/formautofill/test/chrome/.eslintrc b/toolkit/components/formautofill/test/chrome/.eslintrc
deleted file mode 100644
index 218d988742d2..000000000000
--- a/toolkit/components/formautofill/test/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/components/formautofill/test/chrome/.eslintrc.js b/toolkit/components/formautofill/test/chrome/.eslintrc.js
new file mode 100644
index 000000000000..8c0f4f574c28
--- /dev/null
+++ b/toolkit/components/formautofill/test/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/formautofill/test/xpcshell/.eslintrc b/toolkit/components/formautofill/test/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/formautofill/test/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/formautofill/test/xpcshell/.eslintrc.js b/toolkit/components/formautofill/test/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/formautofill/test/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/jsdownloads/test/browser/.eslintrc b/toolkit/components/jsdownloads/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/jsdownloads/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/jsdownloads/test/browser/.eslintrc.js b/toolkit/components/jsdownloads/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/jsdownloads/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/jsdownloads/test/data/.eslintrc b/toolkit/components/jsdownloads/test/data/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/jsdownloads/test/data/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/jsdownloads/test/data/.eslintrc.js b/toolkit/components/jsdownloads/test/data/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/jsdownloads/test/data/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/jsdownloads/test/unit/.eslintrc b/toolkit/components/jsdownloads/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/jsdownloads/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/jsdownloads/test/unit/.eslintrc.js b/toolkit/components/jsdownloads/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/jsdownloads/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/lz4/tests/xpcshell/.eslintrc b/toolkit/components/lz4/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/lz4/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/lz4/tests/xpcshell/.eslintrc.js b/toolkit/components/lz4/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/lz4/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/mediasniffer/test/unit/.eslintrc b/toolkit/components/mediasniffer/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/mediasniffer/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/mediasniffer/test/unit/.eslintrc.js b/toolkit/components/mediasniffer/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/mediasniffer/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/narrate/.eslintrc b/toolkit/components/narrate/.eslintrc.js
similarity index 96%
rename from toolkit/components/narrate/.eslintrc
rename to toolkit/components/narrate/.eslintrc.js
index bb861244eac6..c204af14cb52 100644
--- a/toolkit/components/narrate/.eslintrc
+++ b/toolkit/components/narrate/.eslintrc.js
@@ -1,6 +1,8 @@
-{
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
   "extends": [
-    "../../.eslintrc"
+    "../../.eslintrc.js"
   ],
 
   "globals": {
@@ -89,4 +91,4 @@
     "valid-typeof": 2,
     "yoda": 2
   }
-}
+};
diff --git a/toolkit/components/narrate/test/.eslintrc b/toolkit/components/narrate/test/.eslintrc.js
similarity index 77%
rename from toolkit/components/narrate/test/.eslintrc
rename to toolkit/components/narrate/test/.eslintrc.js
index 9a8bdc2fa820..b8a7eed782be 100644
--- a/toolkit/components/narrate/test/.eslintrc
+++ b/toolkit/components/narrate/test/.eslintrc.js
@@ -1,6 +1,8 @@
-{
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
   "extends": [
-    "../.eslintrc"
+    "../.eslintrc.js"
   ],
 
   "globals": {
@@ -18,4 +20,4 @@
   "rules": {
     "mozilla/import-headjs-globals": 1
   }
-}
+};
diff --git a/toolkit/components/osfile/tests/mochi/.eslintrc b/toolkit/components/osfile/tests/mochi/.eslintrc
deleted file mode 100644
index 218d988742d2..000000000000
--- a/toolkit/components/osfile/tests/mochi/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/components/osfile/tests/mochi/.eslintrc.js b/toolkit/components/osfile/tests/mochi/.eslintrc.js
new file mode 100644
index 000000000000..8c0f4f574c28
--- /dev/null
+++ b/toolkit/components/osfile/tests/mochi/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/osfile/tests/xpcshell/.eslintrc b/toolkit/components/osfile/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/osfile/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/osfile/tests/xpcshell/.eslintrc.js b/toolkit/components/osfile/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/osfile/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/passwordmgr/.eslintrc b/toolkit/components/passwordmgr/.eslintrc.js
similarity index 89%
rename from toolkit/components/passwordmgr/.eslintrc
rename to toolkit/components/passwordmgr/.eslintrc.js
index 1379e4f7520b..33bc1e98f5dd 100644
--- a/toolkit/components/passwordmgr/.eslintrc
+++ b/toolkit/components/passwordmgr/.eslintrc.js
@@ -1,5 +1,7 @@
-{
-  "extends": "../../.eslintrc",
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../.eslintrc.js",
   "rules": {
     // Require spacing around =>
     "arrow-spacing": 2,
@@ -31,4 +33,4 @@
     // Require spaces around operators
     "space-infix-ops": 2,
   }
-}
+};
diff --git a/toolkit/components/passwordmgr/test/.eslintrc b/toolkit/components/passwordmgr/test/.eslintrc
deleted file mode 100644
index 6c4908066032..000000000000
--- a/toolkit/components/passwordmgr/test/.eslintrc
+++ /dev/null
@@ -1,11 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/mochitest.eslintrc",
-    "../../../../testing/mochitest/chrome.eslintrc"
-  ],
-  "rules": {
-    "brace-style": 0,
-    "no-undef": 0,
-    "no-unused-vars": 0,
-  },
-}
diff --git a/toolkit/components/passwordmgr/test/.eslintrc.js b/toolkit/components/passwordmgr/test/.eslintrc.js
new file mode 100644
index 000000000000..7cc1073304bd
--- /dev/null
+++ b/toolkit/components/passwordmgr/test/.eslintrc.js
@@ -0,0 +1,13 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": [
+    "../../../../testing/mochitest/mochitest.eslintrc.js",
+    "../../../../testing/mochitest/chrome.eslintrc.js"
+  ],
+  "rules": {
+    "brace-style": 0,
+    "no-undef": 0,
+    "no-unused-vars": 0,
+  },
+};
diff --git a/toolkit/components/passwordmgr/test/browser/.eslintrc b/toolkit/components/passwordmgr/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/passwordmgr/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/passwordmgr/test/browser/.eslintrc.js b/toolkit/components/passwordmgr/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/passwordmgr/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/passwordmgr/test/unit/.eslintrc b/toolkit/components/passwordmgr/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/passwordmgr/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/passwordmgr/test/unit/.eslintrc.js b/toolkit/components/passwordmgr/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/passwordmgr/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/perf/.eslintrc b/toolkit/components/perf/.eslintrc
deleted file mode 100644
index e617dcd2f8a4..000000000000
--- a/toolkit/components/perf/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/components/perf/.eslintrc.js b/toolkit/components/perf/.eslintrc.js
new file mode 100644
index 000000000000..4e6d4bcf08e2
--- /dev/null
+++ b/toolkit/components/perf/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/perfmonitoring/tests/browser/.eslintrc b/toolkit/components/perfmonitoring/tests/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/perfmonitoring/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/perfmonitoring/tests/browser/.eslintrc.js b/toolkit/components/perfmonitoring/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/perfmonitoring/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/.eslintrc b/toolkit/components/places/tests/.eslintrc
deleted file mode 100644
index 9d2c1e5feafe..000000000000
--- a/toolkit/components/places/tests/.eslintrc
+++ /dev/null
@@ -1,7 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/mochitest.eslintrc",
-    "../../../../testing/mochitest/chrome.eslintrc",
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/.eslintrc.js b/toolkit/components/places/tests/.eslintrc.js
new file mode 100644
index 000000000000..d5283c9665bf
--- /dev/null
+++ b/toolkit/components/places/tests/.eslintrc.js
@@ -0,0 +1,9 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/mochitest.eslintrc.js",
+    "../../../../testing/mochitest/chrome.eslintrc.js",
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/bookmarks/.eslintrc b/toolkit/components/places/tests/bookmarks/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/places/tests/bookmarks/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/bookmarks/.eslintrc.js b/toolkit/components/places/tests/bookmarks/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/places/tests/bookmarks/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/browser/.eslintrc b/toolkit/components/places/tests/browser/.eslintrc
deleted file mode 100644
index cfb2f1f30455..000000000000
--- a/toolkit/components/places/tests/browser/.eslintrc
+++ /dev/null
@@ -1,6 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc",
-    "../../../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/browser/.eslintrc.js b/toolkit/components/places/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..7a41a9cde026
--- /dev/null
+++ b/toolkit/components/places/tests/browser/.eslintrc.js
@@ -0,0 +1,8 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js",
+    "../../../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/chrome/.eslintrc b/toolkit/components/places/tests/chrome/.eslintrc
deleted file mode 100644
index 052b243417a2..000000000000
--- a/toolkit/components/places/tests/chrome/.eslintrc
+++ /dev/null
@@ -1,6 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc",
-    "../../../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/chrome/.eslintrc.js b/toolkit/components/places/tests/chrome/.eslintrc.js
new file mode 100644
index 000000000000..bf379df8dfeb
--- /dev/null
+++ b/toolkit/components/places/tests/chrome/.eslintrc.js
@@ -0,0 +1,8 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js",
+    "../../../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/expiration/.eslintrc b/toolkit/components/places/tests/expiration/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/places/tests/expiration/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/expiration/.eslintrc.js b/toolkit/components/places/tests/expiration/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/places/tests/expiration/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/favicons/.eslintrc b/toolkit/components/places/tests/favicons/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/places/tests/favicons/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/favicons/.eslintrc.js b/toolkit/components/places/tests/favicons/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/places/tests/favicons/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/history/.eslintrc b/toolkit/components/places/tests/history/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/places/tests/history/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/history/.eslintrc.js b/toolkit/components/places/tests/history/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/places/tests/history/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/migration/.eslintrc b/toolkit/components/places/tests/migration/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/places/tests/migration/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/migration/.eslintrc.js b/toolkit/components/places/tests/migration/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/places/tests/migration/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/network/.eslintrc b/toolkit/components/places/tests/network/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/places/tests/network/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/network/.eslintrc.js b/toolkit/components/places/tests/network/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/places/tests/network/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/queries/.eslintrc b/toolkit/components/places/tests/queries/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/places/tests/queries/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/queries/.eslintrc.js b/toolkit/components/places/tests/queries/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/places/tests/queries/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/unifiedcomplete/.eslintrc b/toolkit/components/places/tests/unifiedcomplete/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/places/tests/unifiedcomplete/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/unifiedcomplete/.eslintrc.js b/toolkit/components/places/tests/unifiedcomplete/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/places/tests/unifiedcomplete/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/places/tests/unit/.eslintrc b/toolkit/components/places/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/places/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/places/tests/unit/.eslintrc.js b/toolkit/components/places/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/places/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/promiseworker/tests/xpcshell/.eslintrc b/toolkit/components/promiseworker/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/promiseworker/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/promiseworker/tests/xpcshell/.eslintrc.js b/toolkit/components/promiseworker/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/promiseworker/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/prompts/test/.eslintrc b/toolkit/components/prompts/test/.eslintrc
deleted file mode 100644
index 9174183fccce..000000000000
--- a/toolkit/components/prompts/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/toolkit/components/prompts/test/.eslintrc.js b/toolkit/components/prompts/test/.eslintrc.js
new file mode 100644
index 000000000000..3c788d6d681c
--- /dev/null
+++ b/toolkit/components/prompts/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/remotebrowserutils/tests/browser/.eslintrc b/toolkit/components/remotebrowserutils/tests/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/remotebrowserutils/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/remotebrowserutils/tests/browser/.eslintrc.js b/toolkit/components/remotebrowserutils/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/remotebrowserutils/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/satchel/test/.eslintrc b/toolkit/components/satchel/test/.eslintrc
deleted file mode 100644
index 9174183fccce..000000000000
--- a/toolkit/components/satchel/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/toolkit/components/satchel/test/.eslintrc.js b/toolkit/components/satchel/test/.eslintrc.js
new file mode 100644
index 000000000000..3c788d6d681c
--- /dev/null
+++ b/toolkit/components/satchel/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/satchel/test/browser/.eslintrc b/toolkit/components/satchel/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/satchel/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/satchel/test/browser/.eslintrc.js b/toolkit/components/satchel/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/satchel/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/satchel/test/unit/.eslintrc b/toolkit/components/satchel/test/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/satchel/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/satchel/test/unit/.eslintrc.js b/toolkit/components/satchel/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/satchel/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/search/tests/xpcshell/.eslintrc b/toolkit/components/search/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/search/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/search/tests/xpcshell/.eslintrc.js b/toolkit/components/search/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/search/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/social/test/xpcshell/.eslintrc b/toolkit/components/social/test/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/social/test/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/social/test/xpcshell/.eslintrc.js b/toolkit/components/social/test/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/social/test/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/sqlite/tests/xpcshell/.eslintrc b/toolkit/components/sqlite/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/sqlite/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/sqlite/tests/xpcshell/.eslintrc.js b/toolkit/components/sqlite/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/sqlite/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/startup/tests/browser/.eslintrc b/toolkit/components/startup/tests/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/startup/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/startup/tests/browser/.eslintrc.js b/toolkit/components/startup/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/startup/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/startup/tests/unit/.eslintrc b/toolkit/components/startup/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/startup/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/startup/tests/unit/.eslintrc.js b/toolkit/components/startup/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/startup/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/telemetry/tests/unit/.eslintrc b/toolkit/components/telemetry/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/telemetry/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/telemetry/tests/unit/.eslintrc.js b/toolkit/components/telemetry/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/telemetry/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/terminator/tests/xpcshell/.eslintrc b/toolkit/components/terminator/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/terminator/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/terminator/tests/xpcshell/.eslintrc.js b/toolkit/components/terminator/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/terminator/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/thumbnails/test/.eslintrc b/toolkit/components/thumbnails/test/.eslintrc
deleted file mode 100644
index 9671781eda59..000000000000
--- a/toolkit/components/thumbnails/test/.eslintrc
+++ /dev/null
@@ -1,6 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc",
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/thumbnails/test/.eslintrc.js b/toolkit/components/thumbnails/test/.eslintrc.js
new file mode 100644
index 000000000000..f6f8d62c2437
--- /dev/null
+++ b/toolkit/components/thumbnails/test/.eslintrc.js
@@ -0,0 +1,8 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js",
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/timermanager/tests/unit/.eslintrc b/toolkit/components/timermanager/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/timermanager/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/timermanager/tests/unit/.eslintrc.js b/toolkit/components/timermanager/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/timermanager/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/url-classifier/tests/mochitest/.eslintrc b/toolkit/components/url-classifier/tests/mochitest/.eslintrc
deleted file mode 100644
index 67d97e14fc20..000000000000
--- a/toolkit/components/url-classifier/tests/mochitest/.eslintrc
+++ /dev/null
@@ -1,6 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/mochitest.eslintrc",
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/components/url-classifier/tests/mochitest/.eslintrc.js b/toolkit/components/url-classifier/tests/mochitest/.eslintrc.js
new file mode 100644
index 000000000000..58b3df4a7405
--- /dev/null
+++ b/toolkit/components/url-classifier/tests/mochitest/.eslintrc.js
@@ -0,0 +1,8 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/mochitest.eslintrc.js",
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/url-classifier/tests/unit/.eslintrc b/toolkit/components/url-classifier/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/url-classifier/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/url-classifier/tests/unit/.eslintrc.js b/toolkit/components/url-classifier/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/url-classifier/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/urlformatter/tests/unit/.eslintrc b/toolkit/components/urlformatter/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/urlformatter/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/urlformatter/tests/unit/.eslintrc.js b/toolkit/components/urlformatter/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/urlformatter/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/viewsource/test/.eslintrc b/toolkit/components/viewsource/test/.eslintrc
deleted file mode 100644
index e2b648435bb8..000000000000
--- a/toolkit/components/viewsource/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/components/viewsource/test/.eslintrc.js b/toolkit/components/viewsource/test/.eslintrc.js
new file mode 100644
index 000000000000..2c669d844eb0
--- /dev/null
+++ b/toolkit/components/viewsource/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/viewsource/test/browser/.eslintrc b/toolkit/components/viewsource/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/components/viewsource/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/components/viewsource/test/browser/.eslintrc.js b/toolkit/components/viewsource/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..7c80211924ef
--- /dev/null
+++ b/toolkit/components/viewsource/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/workerloader/tests/.eslintrc b/toolkit/components/workerloader/tests/.eslintrc
deleted file mode 100644
index e2b648435bb8..000000000000
--- a/toolkit/components/workerloader/tests/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/components/workerloader/tests/.eslintrc.js b/toolkit/components/workerloader/tests/.eslintrc.js
new file mode 100644
index 000000000000..2c669d844eb0
--- /dev/null
+++ b/toolkit/components/workerloader/tests/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/xulstore/tests/chrome/.eslintrc b/toolkit/components/xulstore/tests/chrome/.eslintrc
deleted file mode 100644
index 218d988742d2..000000000000
--- a/toolkit/components/xulstore/tests/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/components/xulstore/tests/chrome/.eslintrc.js b/toolkit/components/xulstore/tests/chrome/.eslintrc.js
new file mode 100644
index 000000000000..8c0f4f574c28
--- /dev/null
+++ b/toolkit/components/xulstore/tests/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/components/xulstore/tests/xpcshell/.eslintrc b/toolkit/components/xulstore/tests/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/components/xulstore/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/components/xulstore/tests/xpcshell/.eslintrc.js b/toolkit/components/xulstore/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/components/xulstore/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/content/tests/browser/.eslintrc b/toolkit/content/tests/browser/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/toolkit/content/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/content/tests/browser/.eslintrc.js b/toolkit/content/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/toolkit/content/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/content/tests/chrome/.eslintrc b/toolkit/content/tests/chrome/.eslintrc
deleted file mode 100644
index e2b648435bb8..000000000000
--- a/toolkit/content/tests/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/content/tests/chrome/.eslintrc.js b/toolkit/content/tests/chrome/.eslintrc.js
new file mode 100644
index 000000000000..2c669d844eb0
--- /dev/null
+++ b/toolkit/content/tests/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/content/tests/unit/.eslintrc b/toolkit/content/tests/unit/.eslintrc
deleted file mode 100644
index 78141af911f7..000000000000
--- a/toolkit/content/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/content/tests/unit/.eslintrc.js b/toolkit/content/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..fee088c17903
--- /dev/null
+++ b/toolkit/content/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/content/tests/widgets/.eslintrc b/toolkit/content/tests/widgets/.eslintrc
deleted file mode 100644
index 590eaa4aafee..000000000000
--- a/toolkit/content/tests/widgets/.eslintrc
+++ /dev/null
@@ -1,6 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/mochitest.eslintrc",
-    "../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/content/tests/widgets/.eslintrc.js b/toolkit/content/tests/widgets/.eslintrc.js
new file mode 100644
index 000000000000..e149193751d8
--- /dev/null
+++ b/toolkit/content/tests/widgets/.eslintrc.js
@@ -0,0 +1,8 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/mochitest.eslintrc.js",
+    "../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/crashreporter/test/browser/.eslintrc b/toolkit/crashreporter/test/browser/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/toolkit/crashreporter/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/crashreporter/test/browser/.eslintrc.js b/toolkit/crashreporter/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/toolkit/crashreporter/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/crashreporter/test/unit/.eslintrc b/toolkit/crashreporter/test/unit/.eslintrc
deleted file mode 100644
index 78141af911f7..000000000000
--- a/toolkit/crashreporter/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/crashreporter/test/unit/.eslintrc.js b/toolkit/crashreporter/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..fee088c17903
--- /dev/null
+++ b/toolkit/crashreporter/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/crashreporter/test/unit_ipc/.eslintrc b/toolkit/crashreporter/test/unit_ipc/.eslintrc
deleted file mode 100644
index 78141af911f7..000000000000
--- a/toolkit/crashreporter/test/unit_ipc/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/crashreporter/test/unit_ipc/.eslintrc.js b/toolkit/crashreporter/test/unit_ipc/.eslintrc.js
new file mode 100644
index 000000000000..fee088c17903
--- /dev/null
+++ b/toolkit/crashreporter/test/unit_ipc/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/forgetaboutsite/test/browser/.eslintrc b/toolkit/forgetaboutsite/test/browser/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/toolkit/forgetaboutsite/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/forgetaboutsite/test/browser/.eslintrc.js b/toolkit/forgetaboutsite/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/toolkit/forgetaboutsite/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/forgetaboutsite/test/unit/.eslintrc b/toolkit/forgetaboutsite/test/unit/.eslintrc
deleted file mode 100644
index 78141af911f7..000000000000
--- a/toolkit/forgetaboutsite/test/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/forgetaboutsite/test/unit/.eslintrc.js b/toolkit/forgetaboutsite/test/unit/.eslintrc.js
new file mode 100644
index 000000000000..fee088c17903
--- /dev/null
+++ b/toolkit/forgetaboutsite/test/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/identity/tests/chrome/.eslintrc b/toolkit/identity/tests/chrome/.eslintrc
deleted file mode 100644
index e2b648435bb8..000000000000
--- a/toolkit/identity/tests/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/identity/tests/chrome/.eslintrc.js b/toolkit/identity/tests/chrome/.eslintrc.js
new file mode 100644
index 000000000000..2c669d844eb0
--- /dev/null
+++ b/toolkit/identity/tests/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/identity/tests/unit/.eslintrc b/toolkit/identity/tests/unit/.eslintrc
deleted file mode 100644
index 78141af911f7..000000000000
--- a/toolkit/identity/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/identity/tests/unit/.eslintrc.js b/toolkit/identity/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..fee088c17903
--- /dev/null
+++ b/toolkit/identity/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/modules/addons/.eslintrc b/toolkit/modules/addons/.eslintrc.js
similarity index 59%
rename from toolkit/modules/addons/.eslintrc
rename to toolkit/modules/addons/.eslintrc.js
index 4557ca65c458..32c92be0adf5 100644
--- a/toolkit/modules/addons/.eslintrc
+++ b/toolkit/modules/addons/.eslintrc.js
@@ -1,5 +1,7 @@
-{
-  "extends": "../../components/extensions/.eslintrc",
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../components/extensions/.eslintrc.js",
 
   "globals": {
     "addEventListener": false,
@@ -9,4 +11,4 @@
 
     "initialProcessData": true,
   },
-}
+};
diff --git a/toolkit/modules/subprocess/.eslintrc b/toolkit/modules/subprocess/.eslintrc.js
similarity index 73%
rename from toolkit/modules/subprocess/.eslintrc
rename to toolkit/modules/subprocess/.eslintrc.js
index ce2ff918dfd8..2ddebba69fa6 100644
--- a/toolkit/modules/subprocess/.eslintrc
+++ b/toolkit/modules/subprocess/.eslintrc.js
@@ -1,5 +1,7 @@
-{
-  "extends": "../../components/extensions/.eslintrc",
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../components/extensions/.eslintrc.js",
 
   "env": {
     "worker": true,
@@ -23,4 +25,4 @@
   "rules": {
     "no-console": 0,
   },
-}
+};
diff --git a/toolkit/modules/subprocess/test/xpcshell/.eslintrc b/toolkit/modules/subprocess/test/xpcshell/.eslintrc
deleted file mode 100644
index 60fdab2176e8..000000000000
--- a/toolkit/modules/subprocess/test/xpcshell/.eslintrc
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-  "extends": "../../../../../testing/xpcshell/xpcshell.eslintrc",
-}
diff --git a/toolkit/modules/subprocess/test/xpcshell/.eslintrc.js b/toolkit/modules/subprocess/test/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..fc63a79b75a3
--- /dev/null
+++ b/toolkit/modules/subprocess/test/xpcshell/.eslintrc.js
@@ -0,0 +1,5 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": "../../../../../testing/xpcshell/xpcshell.eslintrc.js",
+};
diff --git a/toolkit/modules/tests/browser/.eslintrc b/toolkit/modules/tests/browser/.eslintrc
deleted file mode 100644
index f4517b89b361..000000000000
--- a/toolkit/modules/tests/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/modules/tests/browser/.eslintrc.js b/toolkit/modules/tests/browser/.eslintrc.js
new file mode 100644
index 000000000000..c764b133dc9c
--- /dev/null
+++ b/toolkit/modules/tests/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/modules/tests/chrome/.eslintrc b/toolkit/modules/tests/chrome/.eslintrc
deleted file mode 100644
index e2b648435bb8..000000000000
--- a/toolkit/modules/tests/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/modules/tests/chrome/.eslintrc.js b/toolkit/modules/tests/chrome/.eslintrc.js
new file mode 100644
index 000000000000..2c669d844eb0
--- /dev/null
+++ b/toolkit/modules/tests/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/modules/tests/mochitest/.eslintrc b/toolkit/modules/tests/mochitest/.eslintrc
deleted file mode 100644
index 9174183fccce..000000000000
--- a/toolkit/modules/tests/mochitest/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/toolkit/modules/tests/mochitest/.eslintrc.js b/toolkit/modules/tests/mochitest/.eslintrc.js
new file mode 100644
index 000000000000..3c788d6d681c
--- /dev/null
+++ b/toolkit/modules/tests/mochitest/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/toolkit/modules/tests/xpcshell/.eslintrc b/toolkit/modules/tests/xpcshell/.eslintrc
deleted file mode 100644
index 78141af911f7..000000000000
--- a/toolkit/modules/tests/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/modules/tests/xpcshell/.eslintrc.js b/toolkit/modules/tests/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..fee088c17903
--- /dev/null
+++ b/toolkit/modules/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/downloads/tests/chrome/.eslintrc b/toolkit/mozapps/downloads/tests/chrome/.eslintrc
deleted file mode 100644
index 218d988742d2..000000000000
--- a/toolkit/mozapps/downloads/tests/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/downloads/tests/chrome/.eslintrc.js b/toolkit/mozapps/downloads/tests/chrome/.eslintrc.js
new file mode 100644
index 000000000000..8c0f4f574c28
--- /dev/null
+++ b/toolkit/mozapps/downloads/tests/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/downloads/tests/unit/.eslintrc b/toolkit/mozapps/downloads/tests/unit/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/mozapps/downloads/tests/unit/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/downloads/tests/unit/.eslintrc.js b/toolkit/mozapps/downloads/tests/unit/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/mozapps/downloads/tests/unit/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/extensions/.eslintrc b/toolkit/mozapps/extensions/.eslintrc.js
similarity index 51%
rename from toolkit/mozapps/extensions/.eslintrc
rename to toolkit/mozapps/extensions/.eslintrc.js
index 7b630ad3b5af..107f3507676e 100644
--- a/toolkit/mozapps/extensions/.eslintrc
+++ b/toolkit/mozapps/extensions/.eslintrc.js
@@ -1,6 +1,8 @@
-{
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
   "rules": {
     // No using undeclared variables
     "no-undef": 2,
   }
-}
+};
diff --git a/toolkit/mozapps/extensions/test/browser/.eslintrc b/toolkit/mozapps/extensions/test/browser/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/mozapps/extensions/test/browser/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/extensions/test/browser/.eslintrc.js b/toolkit/mozapps/extensions/test/browser/.eslintrc.js
new file mode 100644
index 000000000000..2852eb81d188
--- /dev/null
+++ b/toolkit/mozapps/extensions/test/browser/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/extensions/test/mochitest/.eslintrc b/toolkit/mozapps/extensions/test/mochitest/.eslintrc
deleted file mode 100644
index 81ae1b0f9207..000000000000
--- a/toolkit/mozapps/extensions/test/mochitest/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/extensions/test/mochitest/.eslintrc.js b/toolkit/mozapps/extensions/test/mochitest/.eslintrc.js
new file mode 100644
index 000000000000..383da0f41edd
--- /dev/null
+++ b/toolkit/mozapps/extensions/test/mochitest/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": [
+    "../../../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/extensions/test/xpcshell/.eslintrc b/toolkit/mozapps/extensions/test/xpcshell/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/mozapps/extensions/test/xpcshell/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/extensions/test/xpcshell/.eslintrc.js b/toolkit/mozapps/extensions/test/xpcshell/.eslintrc.js
new file mode 100644
index 000000000000..ba65517f95f2
--- /dev/null
+++ b/toolkit/mozapps/extensions/test/xpcshell/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/extensions/test/xpinstall/.eslintrc b/toolkit/mozapps/extensions/test/xpinstall/.eslintrc
deleted file mode 100644
index be7c552e0ce0..000000000000
--- a/toolkit/mozapps/extensions/test/xpinstall/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/browser.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/extensions/test/xpinstall/.eslintrc.js b/toolkit/mozapps/extensions/test/xpinstall/.eslintrc.js
new file mode 100644
index 000000000000..2852eb81d188
--- /dev/null
+++ b/toolkit/mozapps/extensions/test/xpinstall/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = { // eslint-disable-line no-undef
+  "extends": [
+    "../../../../../testing/mochitest/browser.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/update/tests/chrome/.eslintrc b/toolkit/mozapps/update/tests/chrome/.eslintrc
deleted file mode 100644
index 218d988742d2..000000000000
--- a/toolkit/mozapps/update/tests/chrome/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/update/tests/chrome/.eslintrc.js b/toolkit/mozapps/update/tests/chrome/.eslintrc.js
new file mode 100644
index 000000000000..8c0f4f574c28
--- /dev/null
+++ b/toolkit/mozapps/update/tests/chrome/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/update/tests/unit_aus_update/.eslintrc b/toolkit/mozapps/update/tests/unit_aus_update/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/mozapps/update/tests/unit_aus_update/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/update/tests/unit_aus_update/.eslintrc.js b/toolkit/mozapps/update/tests/unit_aus_update/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/mozapps/update/tests/unit_aus_update/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/update/tests/unit_base_updater/.eslintrc b/toolkit/mozapps/update/tests/unit_base_updater/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/mozapps/update/tests/unit_base_updater/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/update/tests/unit_base_updater/.eslintrc.js b/toolkit/mozapps/update/tests/unit_base_updater/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/mozapps/update/tests/unit_base_updater/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/mozapps/update/tests/unit_service_updater/.eslintrc b/toolkit/mozapps/update/tests/unit_service_updater/.eslintrc
deleted file mode 100644
index 8a895f93bd06..000000000000
--- a/toolkit/mozapps/update/tests/unit_service_updater/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../../testing/xpcshell/xpcshell.eslintrc"
-  ]
-}
diff --git a/toolkit/mozapps/update/tests/unit_service_updater/.eslintrc.js b/toolkit/mozapps/update/tests/unit_service_updater/.eslintrc.js
new file mode 100644
index 000000000000..d35787cd2c49
--- /dev/null
+++ b/toolkit/mozapps/update/tests/unit_service_updater/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../../testing/xpcshell/xpcshell.eslintrc.js"
+  ]
+};
diff --git a/toolkit/profile/test/.eslintrc b/toolkit/profile/test/.eslintrc
deleted file mode 100644
index e617dcd2f8a4..000000000000
--- a/toolkit/profile/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/profile/test/.eslintrc.js b/toolkit/profile/test/.eslintrc.js
new file mode 100644
index 000000000000..4e6d4bcf08e2
--- /dev/null
+++ b/toolkit/profile/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/themes/osx/mochitests/.eslintrc b/toolkit/themes/osx/mochitests/.eslintrc
deleted file mode 100644
index e2b648435bb8..000000000000
--- a/toolkit/themes/osx/mochitests/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../../testing/mochitest/chrome.eslintrc"
-  ]
-}
diff --git a/toolkit/themes/osx/mochitests/.eslintrc.js b/toolkit/themes/osx/mochitests/.eslintrc.js
new file mode 100644
index 000000000000..2c669d844eb0
--- /dev/null
+++ b/toolkit/themes/osx/mochitests/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../../testing/mochitest/chrome.eslintrc.js"
+  ]
+};
diff --git a/toolkit/xre/test/.eslintrc b/toolkit/xre/test/.eslintrc
deleted file mode 100644
index 979bb599a667..000000000000
--- a/toolkit/xre/test/.eslintrc
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-  "extends": [
-    "../../../testing/mochitest/mochitest.eslintrc"
-  ]
-}
diff --git a/toolkit/xre/test/.eslintrc.js b/toolkit/xre/test/.eslintrc.js
new file mode 100644
index 000000000000..e3134a291cc0
--- /dev/null
+++ b/toolkit/xre/test/.eslintrc.js
@@ -0,0 +1,7 @@
+"use strict";
+
+module.exports = {
+  "extends": [
+    "../../../testing/mochitest/mochitest.eslintrc.js"
+  ]
+};
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/.eslintrc b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/.eslintrc.js
similarity index 97%
rename from tools/lint/eslint/eslint-plugin-mozilla/lib/rules/.eslintrc
rename to tools/lint/eslint/eslint-plugin-mozilla/lib/rules/.eslintrc.js
index c9e8c756bf71..e5531cad74ef 100644
--- a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/.eslintrc
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/.eslintrc.js
@@ -1,3 +1,5 @@
+"use strict";
+
 /**
  * Based on npm coding standards at https://docs.npmjs.com/misc/coding-style.
  *
@@ -7,7 +9,7 @@
  *   - Functions should not have whitespace before params.
  */
 
-{
+module.exports = {
   "env": {
     "node": true
   },
@@ -46,4 +48,4 @@
     "DTRACE_NET_STREAM_END": true,
     "Intl": true,
   },
-}
+};