diff --git a/.eslintrc.js b/.eslintrc.js
index e371be682336..48c39ce27f6d 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -355,7 +355,6 @@ module.exports = {
         "no-nested-ternary": "off",
         "no-new-object": "off",
         "no-new-wrappers": "off",
-        "no-octal": "off",
         "no-redeclare": "off",
         "no-return-await": "off",
         "no-restricted-globals": "off",
@@ -474,7 +473,6 @@ module.exports = {
         "no-empty": "off",
         "no-eval": "off",
         "no-lone-blocks": "off",
-        "no-octal": "off",
         "no-redeclare": "off",
         "no-shadow": "off",
         "no-throw-literal": "off",
diff --git a/dom/fetch/tests/browser_blobFromFile.js b/dom/fetch/tests/browser_blobFromFile.js
index 80c9a13113a7..64a34a72d622 100644
--- a/dom/fetch/tests/browser_blobFromFile.js
+++ b/dom/fetch/tests/browser_blobFromFile.js
@@ -21,7 +21,7 @@ add_task(async function test() {
   outStream.init(
     file,
     0x02 | 0x08 | 0x20, // write, create, truncate
-    0666,
+    0o666,
     0
   );
   outStream.write(fileData, fileData.length);
diff --git a/dom/file/ipc/tests/script_file.js b/dom/file/ipc/tests/script_file.js
index d3147a9b1642..56defe1f0b7e 100644
--- a/dom/file/ipc/tests/script_file.js
+++ b/dom/file/ipc/tests/script_file.js
@@ -14,7 +14,7 @@ addMessageListener("file.open", function(e) {
   outStream.init(
     testFile,
     0x02 | 0x08 | 0x20, // write, create, truncate
-    0666,
+    0o666,
     0
   );
 
@@ -41,7 +41,7 @@ addMessageListener("emptyfile.open", function(e) {
   outStream.init(
     testFile,
     0x02 | 0x08 | 0x20, // write, create, truncate
-    0666,
+    0o666,
     0
   );
 
diff --git a/dom/file/tests/test_createFile.js b/dom/file/tests/test_createFile.js
index 046d62ded752..cfdb356b0bbe 100644
--- a/dom/file/tests/test_createFile.js
+++ b/dom/file/tests/test_createFile.js
@@ -17,7 +17,7 @@ add_task(async function() {
   outStream.init(
     existingFile,
     0x02 | 0x08 | 0x20, // write, create, truncate
-    0666,
+    0o666,
     0
   );
 
diff --git a/dom/html/test/forms/test_submit_invalid_file.html b/dom/html/test/forms/test_submit_invalid_file.html
index 33f71b594591..cffce2e2925d 100644
--- a/dom/html/test/forms/test_submit_invalid_file.html
+++ b/dom/html/test/forms/test_submit_invalid_file.html
@@ -37,7 +37,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=702949
 
     var file = FileUtils.getDir("TmpD", [], false);
     file.append("testfile");
-    file.createUnique(SpecialPowers.Ci.nsIFile.NORMAL_FILE_TYPE, 0644);
+    file.createUnique(SpecialPowers.Ci.nsIFile.NORMAL_FILE_TYPE, 0o644);
 
     SpecialPowers.wrap(i).value = file.path;
     file.remove(/* recursive = */ false);
diff --git a/dom/html/test/test_bug658746.html b/dom/html/test/test_bug658746.html
index b3b45e766585..859a92dde579 100644
--- a/dom/html/test/test_bug658746.html
+++ b/dom/html/test/test_bug658746.html
@@ -68,8 +68,8 @@ SetGetDelete(0x3);
 SetGetDelete(0xa);
 
 // Octal numbers as properties.
-SetGetDelete(03);
-SetGetDelete(07);
+SetGetDelete(0o3);
+SetGetDelete(0o7);
 
 // String numbers as properties.
 SetGetDelete('0');
diff --git a/dom/system/tests/test_constants.xhtml b/dom/system/tests/test_constants.xhtml
index e5afc67f1df5..0843d2d327e3 100644
--- a/dom/system/tests/test_constants.xhtml
+++ b/dom/system/tests/test_constants.xhtml
@@ -33,17 +33,17 @@ function test_xul() {
 // Test that OS.Constants.libc is defined
 function test_libc() {
   isnot(null, OS.Constants.libc, "OS.Constants.libc is defined");
-  is(0001, OS.Constants.libc.S_IXOTH, "OS.Constants.libc.S_IXOTH is defined");
-  is(0002, OS.Constants.libc.S_IWOTH, "OS.Constants.libc.S_IWOTH is defined");
-  is(0007, OS.Constants.libc.S_IRWXO, "OS.Constants.libc.S_IRWXO is defined");
-  is(0010, OS.Constants.libc.S_IXGRP, "OS.Constants.libc.S_IXGRP is defined");
-  is(0020, OS.Constants.libc.S_IWGRP, "OS.Constants.libc.S_IWGRP is defined");
-  is(0040, OS.Constants.libc.S_IRGRP, "OS.Constants.libc.S_IRGRP is defined");
-  is(0070, OS.Constants.libc.S_IRWXG, "OS.Constants.libc.S_IRWXG is defined");
-  is(0100, OS.Constants.libc.S_IXUSR, "OS.Constants.libc.S_IXUSR is defined");
-  is(0200, OS.Constants.libc.S_IWUSR, "OS.Constants.libc.S_IWUSR is defined");
-  is(0400, OS.Constants.libc.S_IRUSR, "OS.Constants.libc.S_IRUSR is defined");
-  is(0700, OS.Constants.libc.S_IRWXU, "OS.Constants.libc.S_IRWXU is defined");
+  is(0o001, OS.Constants.libc.S_IXOTH, "OS.Constants.libc.S_IXOTH is defined");
+  is(0o002, OS.Constants.libc.S_IWOTH, "OS.Constants.libc.S_IWOTH is defined");
+  is(0o007, OS.Constants.libc.S_IRWXO, "OS.Constants.libc.S_IRWXO is defined");
+  is(0o010, OS.Constants.libc.S_IXGRP, "OS.Constants.libc.S_IXGRP is defined");
+  is(0o020, OS.Constants.libc.S_IWGRP, "OS.Constants.libc.S_IWGRP is defined");
+  is(0o040, OS.Constants.libc.S_IRGRP, "OS.Constants.libc.S_IRGRP is defined");
+  is(0o070, OS.Constants.libc.S_IRWXG, "OS.Constants.libc.S_IRWXG is defined");
+  is(0o100, OS.Constants.libc.S_IXUSR, "OS.Constants.libc.S_IXUSR is defined");
+  is(0o200, OS.Constants.libc.S_IWUSR, "OS.Constants.libc.S_IWUSR is defined");
+  is(0o400, OS.Constants.libc.S_IRUSR, "OS.Constants.libc.S_IRUSR is defined");
+  is(0o700, OS.Constants.libc.S_IRWXU, "OS.Constants.libc.S_IRWXU is defined");
 }
 
 // Test that OS.Constants.Win is defined
diff --git a/dom/workers/test/test_file.xhtml b/dom/workers/test/test_file.xhtml
index a75045a056e1..2b628e7f4d16 100644
--- a/dom/workers/test/test_file.xhtml
+++ b/dom/workers/test/test_file.xhtml
@@ -41,7 +41,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=123456
     var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
                         .createInstance(Ci.nsIFileOutputStream);
     outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
-                   0666, 0);
+                   0o666, 0);
     outStream.write(fileData, fileData.length);
     outStream.close();
 
diff --git a/dom/workers/test/test_fileBlobPosting.xhtml b/dom/workers/test/test_fileBlobPosting.xhtml
index 060841419cf1..61f4a8e90955 100644
--- a/dom/workers/test/test_fileBlobPosting.xhtml
+++ b/dom/workers/test/test_fileBlobPosting.xhtml
@@ -40,7 +40,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=664783
     var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
                         .createInstance(Ci.nsIFileOutputStream);
     outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
-                   0666, 0);
+                   0o666, 0);
     outStream.write(fileData, fileData.length);
     outStream.close();
 
diff --git a/dom/workers/test/test_fileBlobSubWorker.xhtml b/dom/workers/test/test_fileBlobSubWorker.xhtml
index 00d23f0e0b93..8b6755278831 100644
--- a/dom/workers/test/test_fileBlobSubWorker.xhtml
+++ b/dom/workers/test/test_fileBlobSubWorker.xhtml
@@ -41,7 +41,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=664783
     var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
                         .createInstance(Ci.nsIFileOutputStream);
     outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
-                   0666, 0);
+                   0o666, 0);
     outStream.write(fileData, fileData.length);
     outStream.close();
 
diff --git a/dom/workers/test/test_filePosting.xhtml b/dom/workers/test/test_filePosting.xhtml
index f0d7979c12ae..3ffa219516bc 100644
--- a/dom/workers/test/test_filePosting.xhtml
+++ b/dom/workers/test/test_filePosting.xhtml
@@ -40,7 +40,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=664783
     var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
                         .createInstance(Ci.nsIFileOutputStream);
     outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
-                   0666, 0);
+                   0o666, 0);
     outStream.write(fileData, fileData.length);
     outStream.close();
 
diff --git a/dom/workers/test/test_fileReadSlice.xhtml b/dom/workers/test/test_fileReadSlice.xhtml
index 8ca62d78c5e5..b035fa287215 100644
--- a/dom/workers/test/test_fileReadSlice.xhtml
+++ b/dom/workers/test/test_fileReadSlice.xhtml
@@ -44,7 +44,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=664783
     var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
                         .createInstance(Ci.nsIFileOutputStream);
     outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
-                   0666, 0);
+                   0o666, 0);
     outStream.write(fileData, fileData.length);
     outStream.close();
 
diff --git a/dom/workers/test/test_fileReaderSync.xhtml b/dom/workers/test/test_fileReaderSync.xhtml
index 9eafea31a14b..7cdcaed791e2 100644
--- a/dom/workers/test/test_fileReaderSync.xhtml
+++ b/dom/workers/test/test_fileReaderSync.xhtml
@@ -41,7 +41,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=664783
     var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
                         .createInstance(Ci.nsIFileOutputStream);
     outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
-                   0666, 0);
+                   0o666, 0);
     outStream.write(fileData, fileData.length);
     outStream.close();
 
diff --git a/dom/workers/test/test_fileReaderSyncErrors.xhtml b/dom/workers/test/test_fileReaderSyncErrors.xhtml
index e2b48dd43266..626b67e1baac 100644
--- a/dom/workers/test/test_fileReaderSyncErrors.xhtml
+++ b/dom/workers/test/test_fileReaderSyncErrors.xhtml
@@ -40,7 +40,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=664783
     var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
                         .createInstance(Ci.nsIFileOutputStream);
     outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
-                   0666, 0);
+                   0o666, 0);
     outStream.write(fileData, fileData.length);
     outStream.close();
 
diff --git a/dom/workers/test/test_fileSlice.xhtml b/dom/workers/test/test_fileSlice.xhtml
index 371b7e537692..b683db2ec9d4 100644
--- a/dom/workers/test/test_fileSlice.xhtml
+++ b/dom/workers/test/test_fileSlice.xhtml
@@ -41,7 +41,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=664783
     var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
                         .createInstance(Ci.nsIFileOutputStream);
     outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
-                   0666, 0);
+                   0o666, 0);
     outStream.write(fileData, fileData.length);
     outStream.close();
 
diff --git a/dom/workers/test/test_fileSubWorker.xhtml b/dom/workers/test/test_fileSubWorker.xhtml
index 908b81c88c6b..92aa3b1a171b 100644
--- a/dom/workers/test/test_fileSubWorker.xhtml
+++ b/dom/workers/test/test_fileSubWorker.xhtml
@@ -41,7 +41,7 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=664783
     var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
                         .createInstance(Ci.nsIFileOutputStream);
     outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
-                   0666, 0);
+                   0o666, 0);
     outStream.write(fileData, fileData.length);
     outStream.close();