diff --git a/.eslintignore b/.eslintignore
index 4d1468b70833..d70943eafaff 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -370,6 +370,7 @@ toolkit/components/reader/Readability.js
 toolkit/components/reader/JSDOMParser.js
 
 # Uses preprocessing
+toolkit/components/reader/Readerable.jsm
 toolkit/content/widgets/wizard.xml
 toolkit/modules/AppConstants.jsm
 toolkit/mozapps/update/tests/data/xpcshellConstantsPP.js
diff --git a/browser/actors/AboutReaderChild.jsm b/browser/actors/AboutReaderChild.jsm
index 35300c8b7700..0981e7bcf60f 100644
--- a/browser/actors/AboutReaderChild.jsm
+++ b/browser/actors/AboutReaderChild.jsm
@@ -12,6 +12,8 @@ ChromeUtils.defineModuleGetter(this, "AboutReader",
                                "resource://gre/modules/AboutReader.jsm");
 ChromeUtils.defineModuleGetter(this, "ReaderMode",
                                "resource://gre/modules/ReaderMode.jsm");
+ChromeUtils.defineModuleGetter(this, "Readerable",
+                               "resource://gre/modules/Readerable.jsm");
 
 class AboutReaderChild extends ActorChild {
   constructor(mm) {
@@ -102,7 +104,7 @@ class AboutReaderChild extends ActorChild {
    * painted is not going to work.
    */
   updateReaderButton(forceNonArticle) {
-    if (!ReaderMode.isEnabledForParseOnLoad || this.isAboutReader ||
+    if (!Readerable.isEnabledForParseOnLoad || this.isAboutReader ||
         !this.content || !(this.content.document instanceof this.content.HTMLDocument) ||
         this.content.document.mozSyntheticDocument) {
       return;
@@ -141,7 +143,7 @@ class AboutReaderChild extends ActorChild {
     this.cancelPotentialPendingReadabilityCheck();
     // Only send updates when there are articles; there's no point updating with
     // |false| all the time.
-    if (ReaderMode.isProbablyReaderable(this.content.document)) {
+    if (Readerable.isProbablyReaderable(this.content.document)) {
       this.mm.sendAsyncMessage("Reader:UpdateReaderButton", { isArticle: true });
     } else if (forceNonArticle) {
       this.mm.sendAsyncMessage("Reader:UpdateReaderButton", { isArticle: false });
diff --git a/browser/base/content/test/performance/browser_startup_content.js b/browser/base/content/test/performance/browser_startup_content.js
index 76c9aaac185e..ed35685b88ce 100644
--- a/browser/base/content/test/performance/browser_startup_content.js
+++ b/browser/base/content/test/performance/browser_startup_content.js
@@ -56,7 +56,7 @@ const whitelist = {
     "resource://gre/modules/ActorChild.jsm",
     "resource://gre/modules/ActorManagerChild.jsm",
     "resource://gre/modules/E10SUtils.jsm",
-    "resource://gre/modules/ReaderMode.jsm",
+    "resource://gre/modules/Readerable.jsm",
     "resource://gre/modules/WebProgressChild.jsm",
 
     // Pocket
diff --git a/mobile/android/chrome/content/content.js b/mobile/android/chrome/content/content.js
index 31108508aad8..7d4f66ef1b79 100644
--- a/mobile/android/chrome/content/content.js
+++ b/mobile/android/chrome/content/content.js
@@ -8,6 +8,7 @@ ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
 
 ChromeUtils.defineModuleGetter(this, "AboutReader", "resource://gre/modules/AboutReader.jsm");
 ChromeUtils.defineModuleGetter(this, "ReaderMode", "resource://gre/modules/ReaderMode.jsm");
+ChromeUtils.defineModuleGetter(this, "Readerable", "resource://gre/modules/Readerable.jsm");
 ChromeUtils.defineModuleGetter(this, "LoginManagerContent", "resource://gre/modules/LoginManagerContent.jsm");
 
 XPCOMUtils.defineLazyGetter(this, "gPipNSSBundle", function() {
@@ -486,7 +487,7 @@ var AboutReaderListener = {
     // Do not show Reader View icon on error pages (bug 1320900)
     if (this.isErrorPage) {
         sendAsyncMessage("Reader:UpdateReaderButton", { isArticle: false });
-    } else if (!ReaderMode.isEnabledForParseOnLoad || this.isAboutReader ||
+    } else if (!Readerable.isEnabledForParseOnLoad || this.isAboutReader ||
         !(content.document instanceof content.HTMLDocument) ||
         content.document.mozSyntheticDocument) {
 
@@ -522,11 +523,12 @@ var AboutReaderListener = {
       return;
     }
 
+    Services.console.logStringMessage(`ON PAINT WHEN WAITED FOR\n`);
     this.cancelPotentialPendingReadabilityCheck();
 
     // Only send updates when there are articles; there's no point updating with
     // |false| all the time.
-    if (ReaderMode.isProbablyReaderable(content.document)) {
+    if (Readerable.isProbablyReaderable(content.document)) {
       sendAsyncMessage("Reader:UpdateReaderButton", { isArticle: true });
     } else if (forceNonArticle) {
       sendAsyncMessage("Reader:UpdateReaderButton", { isArticle: false });
diff --git a/toolkit/components/reader/Readability-readerable.js b/toolkit/components/reader/Readability-readerable.js
new file mode 100644
index 000000000000..f38b418a061b
--- /dev/null
+++ b/toolkit/components/reader/Readability-readerable.js
@@ -0,0 +1,96 @@
+/* eslint-env es6:false */
+/* globals exports */
+/*
+ * Copyright (c) 2010 Arc90 Inc
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * This code is heavily based on Arc90's readability.js (1.7.1) script
+ * available at: http://code.google.com/p/arc90labs-readability
+ */
+
+var REGEXPS = {
+  // NOTE: These two regular expressions are duplicated in
+  // Readability.js. Please keep both copies in sync.
+  unlikelyCandidates: /-ad-|banner|breadcrumbs|combx|comment|community|cover-wrap|disqus|extra|foot|header|legends|menu|related|remark|replies|rss|shoutbox|sidebar|skyscraper|social|sponsor|supplemental|ad-break|agegate|pagination|pager|popup|yom-remote/i,
+  okMaybeItsACandidate: /and|article|body|column|main|shadow/i,
+};
+
+function isNodeVisible(node) {
+  return node.style.display != "none" && !node.hasAttribute("hidden");
+}
+
+/**
+ * Decides whether or not the document is reader-able without parsing the whole thing.
+ *
+ * @return boolean Whether or not we suspect Readability.parse() will suceeed at returning an article object.
+ */
+function isProbablyReaderable(doc, isVisible) {
+  if (!isVisible) {
+    isVisible = isNodeVisible;
+  }
+
+  var nodes = doc.querySelectorAll("p, pre");
+
+  // Get <div> nodes which have <br> node(s) and append them into the `nodes` variable.
+  // Some articles' DOM structures might look like
+  // <div>
+  //   Sentences<br>
+  //   <br>
+  //   Sentences<br>
+  // </div>
+  var brNodes = doc.querySelectorAll("div > br");
+  if (brNodes.length) {
+    var set = new Set(nodes);
+    [].forEach.call(brNodes, function(node) {
+      set.add(node.parentNode);
+    });
+    nodes = Array.from(set);
+  }
+
+  var score = 0;
+  // This is a little cheeky, we use the accumulator 'score' to decide what to return from
+  // this callback:
+  return [].some.call(nodes, function(node) {
+    if (!isVisible(node))
+      return false;
+
+    var matchString = node.className + " " + node.id;
+    if (REGEXPS.unlikelyCandidates.test(matchString) &&
+        !REGEXPS.okMaybeItsACandidate.test(matchString)) {
+      return false;
+    }
+
+    if (node.matches("li p")) {
+      return false;
+    }
+
+    var textContentLength = node.textContent.trim().length;
+    if (textContentLength < 140) {
+      return false;
+    }
+
+    score += Math.sqrt(textContentLength - 140);
+
+    if (score > 20) {
+      return true;
+    }
+    return false;
+  });
+}
+
+if (typeof exports === "object") {
+  exports.isProbablyReaderable = isProbablyReaderable;
+}
diff --git a/toolkit/components/reader/Readability.js b/toolkit/components/reader/Readability.js
index da89277e3718..deac15904d55 100644
--- a/toolkit/components/reader/Readability.js
+++ b/toolkit/components/reader/Readability.js
@@ -1,11 +1,4 @@
 /*eslint-env es6:false*/
-/*
- * DO NOT MODIFY THIS FILE DIRECTLY!
- *
- * This is a shared library that is maintained in an external repo:
- * https://github.com/mozilla/readability
- */
-
 /*
  * Copyright (c) 2010 Arc90 Inc
  *
@@ -118,8 +111,11 @@ Readability.prototype = {
   // All of the regular expressions in use within readability.
   // Defined up here so we don't instantiate them repeatedly in loops.
   REGEXPS: {
+    // NOTE: These two regular expressions are duplicated in
+    // Readability-readerable.js. Please keep both copies in sync.
     unlikelyCandidates: /-ad-|banner|breadcrumbs|combx|comment|community|cover-wrap|disqus|extra|foot|header|legends|menu|related|remark|replies|rss|shoutbox|sidebar|skyscraper|social|sponsor|supplemental|ad-break|agegate|pagination|pager|popup|yom-remote/i,
     okMaybeItsACandidate: /and|article|body|column|main|shadow/i,
+
     positive: /article|body|content|entry|hentry|h-entry|main|page|pagination|post|text|blog|story/i,
     negative: /hidden|^hid$| hid$| hid |^hid |banner|combx|comment|com-|contact|foot|footer|footnote|masthead|media|meta|outbrain|promo|related|scroll|share|shoutbox|sidebar|skyscraper|sponsor|shopping|tags|tool|widget/i,
     extraneous: /print|archive|comment|discuss|e[\-]?mail|share|reply|all|login|sign|single|utility/i,
@@ -1711,65 +1707,6 @@ Readability.prototype = {
     return node.style.display != "none" && !node.hasAttribute("hidden");
   },
 
-  /**
-   * Decides whether or not the document is reader-able without parsing the whole thing.
-   *
-   * @return boolean Whether or not we suspect parse() will suceeed at returning an article object.
-   */
-  isProbablyReaderable: function(helperIsVisible) {
-    var nodes = this._getAllNodesWithTag(this._doc, ["p", "pre"]);
-
-    // Get <div> nodes which have <br> node(s) and append them into the `nodes` variable.
-    // Some articles' DOM structures might look like
-    // <div>
-    //   Sentences<br>
-    //   <br>
-    //   Sentences<br>
-    // </div>
-    var brNodes = this._getAllNodesWithTag(this._doc, ["div > br"]);
-    if (brNodes.length) {
-      var set = new Set();
-      [].forEach.call(brNodes, function(node) {
-        set.add(node.parentNode);
-      });
-      nodes = [].concat.apply(Array.from(set), nodes);
-    }
-
-    if (!helperIsVisible) {
-      helperIsVisible = this._isProbablyVisible;
-    }
-
-    var score = 0;
-    // This is a little cheeky, we use the accumulator 'score' to decide what to return from
-    // this callback:
-    return this._someNode(nodes, function(node) {
-      if (helperIsVisible && !helperIsVisible(node))
-        return false;
-      var matchString = node.className + " " + node.id;
-
-      if (this.REGEXPS.unlikelyCandidates.test(matchString) &&
-          !this.REGEXPS.okMaybeItsACandidate.test(matchString)) {
-        return false;
-      }
-
-      if (node.matches && node.matches("li p")) {
-        return false;
-      }
-
-      var textContentLength = node.textContent.trim().length;
-      if (textContentLength < 140) {
-        return false;
-      }
-
-      score += Math.sqrt(textContentLength - 140);
-
-      if (score > 20) {
-        return true;
-      }
-      return false;
-    });
-  },
-
   /**
    * Runs readability.
    *
diff --git a/toolkit/components/reader/ReaderMode.jsm b/toolkit/components/reader/ReaderMode.jsm
index f147d5a95520..134ca7a6b1af 100644
--- a/toolkit/components/reader/ReaderMode.jsm
+++ b/toolkit/components/reader/ReaderMode.jsm
@@ -41,13 +41,7 @@ ChromeUtils.defineModuleGetter(this, "EventDispatcher", "resource://gre/modules/
 ChromeUtils.defineModuleGetter(this, "OS", "resource://gre/modules/osfile.jsm");
 ChromeUtils.defineModuleGetter(this, "ReaderWorker", "resource://gre/modules/reader/ReaderWorker.jsm");
 ChromeUtils.defineModuleGetter(this, "LanguageDetector", "resource:///modules/translation/LanguageDetector.jsm");
-
-XPCOMUtils.defineLazyGetter(this, "Readability", function() {
-  let scope = {};
-  scope.dump = this.dump;
-  Services.scriptloader.loadSubScript("resource://gre/modules/reader/Readability.js", scope);
-  return scope.Readability;
-});
+ChromeUtils.defineModuleGetter(this, "Readerable", "resource://gre/modules/Readerable.jsm");
 
 const gIsFirefoxDesktop = Services.appinfo.ID == "{ec8030f7-c20a-464f-9b0e-13a3a9e97384}";
 
@@ -57,42 +51,6 @@ var ReaderMode = {
 
   DEBUG: 0,
 
-  // Don't try to parse the page if it has too many elements (for memory and
-  // performance reasons)
-  get maxElemsToParse() {
-    delete this.parseNodeLimit;
-
-    Services.prefs.addObserver("reader.parse-node-limit", this);
-    return this.parseNodeLimit = Services.prefs.getIntPref("reader.parse-node-limit");
-  },
-
-  get isEnabledForParseOnLoad() {
-    delete this.isEnabledForParseOnLoad;
-
-    // Listen for future pref changes.
-    Services.prefs.addObserver("reader.parse-on-load.", this);
-
-    return this.isEnabledForParseOnLoad = this._getStateForParseOnLoad();
-  },
-
-  _getStateForParseOnLoad() {
-    let isEnabled = Services.prefs.getBoolPref("reader.parse-on-load.enabled");
-    let isForceEnabled = Services.prefs.getBoolPref("reader.parse-on-load.force-enabled");
-    return isForceEnabled || isEnabled;
-  },
-
-  observe(aMessage, aTopic, aData) {
-    switch (aTopic) {
-      case "nsPref:changed":
-        if (aData.startsWith("reader.parse-on-load.")) {
-          this.isEnabledForParseOnLoad = this._getStateForParseOnLoad();
-        } else if (aData === "reader.parse-node-limit") {
-          this.parseNodeLimit = Services.prefs.getIntPref(aData);
-        }
-        break;
-    }
-  },
-
   /**
    * Enter the reader mode by going forward one step in history if applicable,
    * if not, append the about:reader page in the history instead.
@@ -197,39 +155,6 @@ var ReaderMode = {
     return null;
   },
 
-  /**
-   * Decides whether or not a document is reader-able without parsing the whole thing.
-   *
-   * @param doc A document to parse.
-   * @return boolean Whether or not we should show the reader mode button.
-   */
-  isProbablyReaderable(doc) {
-    // Only care about 'real' HTML documents:
-    if (doc.mozSyntheticDocument || !(doc instanceof doc.defaultView.HTMLDocument)) {
-      return false;
-    }
-
-    let uri = Services.io.newURI(doc.location.href);
-    if (!this._shouldCheckUri(uri)) {
-      return false;
-    }
-
-    let utils = this.getUtilsForWin(doc.defaultView);
-    // We pass in a helper function to determine if a node is visible, because
-    // it uses gecko APIs that the engine-agnostic readability code can't rely
-    // upon.
-    return new Readability(doc).isProbablyReaderable(this.isNodeVisible.bind(this, utils));
-  },
-
-  isNodeVisible(utils, node) {
-    let bounds = utils.getBoundsWithoutFlushing(node);
-    return bounds.height > 0 && bounds.width > 0;
-  },
-
-  getUtilsForWin(win) {
-    return win.windowUtils;
-  },
-
   /**
    * Gets an article from a loaded browser's document. This method will not attempt
    * to parse certain URIs (e.g. about: URIs).
@@ -239,7 +164,8 @@ var ReaderMode = {
    * @resolves JS object representing the article, or null if no article is found.
    */
   parseDocument(doc) {
-    if (!this._shouldCheckUri(doc.documentURIObject) || !this._shouldCheckUri(doc.baseURIObject, true)) {
+    if (!Readerable.shouldCheckUri(doc.documentURIObject) ||
+        !Readerable.shouldCheckUri(doc.baseURIObject, true)) {
       this.log("Reader mode disabled for URI");
       return null;
     }
@@ -259,7 +185,8 @@ var ReaderMode = {
     if (!doc) {
       return null;
     }
-    if (!this._shouldCheckUri(doc.documentURIObject) || !this._shouldCheckUri(doc.baseURIObject, true)) {
+    if (!Readerable.shouldCheckUri(doc.documentURIObject) ||
+        !Readerable.shouldCheckUri(doc.baseURIObject, true)) {
       this.log("Reader mode disabled for URI");
       return null;
     }
@@ -269,7 +196,7 @@ var ReaderMode = {
 
   _downloadDocument(url) {
     try {
-      if (!this._shouldCheckUri(Services.io.newURI(url))) {
+      if (!Readerable.shouldCheckUri(Services.io.newURI(url))) {
         return null;
       }
     } catch (ex) {
@@ -415,42 +342,6 @@ var ReaderMode = {
       dump("Reader: " + msg);
   },
 
-  _blockedHosts: [
-    "amazon.com",
-    "github.com",
-    "mail.google.com",
-    "pinterest.com",
-    "reddit.com",
-    "twitter.com",
-    "youtube.com",
-  ],
-
-  _shouldCheckUri(uri, isBaseUri = false) {
-    if (!(uri.schemeIs("http") || uri.schemeIs("https"))) {
-      this.log("Not parsing URI scheme: " + uri.scheme);
-      return false;
-    }
-
-    try {
-      uri.QueryInterface(Ci.nsIURL);
-    } catch (ex) {
-      // If this doesn't work, presumably the URL is not well-formed or something
-      return false;
-    }
-    // Sadly, some high-profile pages have false positives, so bail early for those:
-    let asciiHost = uri.asciiHost;
-    if (!isBaseUri && this._blockedHosts.some(blockedHost => asciiHost.endsWith(blockedHost))) {
-      return false;
-    }
-
-    if (!isBaseUri && (!uri.filePath || uri.filePath == "/")) {
-      this.log("Not parsing home page: " + uri.spec);
-      return false;
-    }
-
-    return true;
-  },
-
   /**
    * Attempts to parse a document into an article. Heavy lifting happens
    * in readerWorker.js.
@@ -641,3 +532,6 @@ var ReaderMode = {
     return readingSpeed.get(lang) || readingSpeed.get("en");
   },
 };
+
+XPCOMUtils.defineLazyPreferenceGetter(
+  ReaderMode, "maxElemsToParse", "reader.parse-node-limit", 0);
diff --git a/toolkit/components/reader/Readerable.js b/toolkit/components/reader/Readerable.js
new file mode 100644
index 000000000000..509e53d3f761
--- /dev/null
+++ b/toolkit/components/reader/Readerable.js
@@ -0,0 +1,79 @@
+// -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+// This file and Readability-readerable.js are merged together into
+// Readerable.jsm.
+
+/* exported Readerable */
+/* import-globals-from Readability-readerable.js */
+
+ChromeUtils.import("resource://gre/modules/Services.jsm");
+ChromeUtils.import("resource://gre/modules/XPCOMUtils.jsm");
+
+function isNodeVisible(node) {
+  return node.clientHeight > 0 && node.clientWidth > 0;
+}
+
+var Readerable = {
+  get isEnabledForParseOnLoad() {
+    return this.isEnabled || this.isForceEnabled;
+  },
+
+  /**
+   * Decides whether or not a document is reader-able without parsing the whole thing.
+   *
+   * @param doc A document to parse.
+   * @return boolean Whether or not we should show the reader mode button.
+   */
+  isProbablyReaderable(doc) {
+    // Only care about 'real' HTML documents:
+    if (doc.mozSyntheticDocument || !(doc instanceof doc.defaultView.HTMLDocument)) {
+      return false;
+    }
+
+    let uri = Services.io.newURI(doc.location.href);
+    if (!this.shouldCheckUri(uri)) {
+      return false;
+    }
+
+    return isProbablyReaderable(doc, isNodeVisible);
+  },
+
+  _blockedHosts: [
+    "amazon.com",
+    "github.com",
+    "mail.google.com",
+    "pinterest.com",
+    "reddit.com",
+    "twitter.com",
+    "youtube.com",
+  ],
+
+  shouldCheckUri(uri, isBaseUri = false) {
+    if (!["http", "https"].includes(uri.scheme)) {
+      return false;
+    }
+
+    if (!isBaseUri) {
+      // Sadly, some high-profile pages have false positives, so bail early for those:
+      let {host} = uri;
+      if (this._blockedHosts.some(blockedHost => host.endsWith(blockedHost))) {
+        return false;
+      }
+
+      if (uri.filePath == "/") {
+        return false;
+      }
+    }
+
+    return true;
+  },
+};
+
+XPCOMUtils.defineLazyPreferenceGetter(
+  Readerable, "isEnabled", "reader.parse-on-load.enabled", true);
+XPCOMUtils.defineLazyPreferenceGetter(
+  Readerable, "isForceEnabled", "reader.parse-on-load.force-enabled", false);
diff --git a/toolkit/components/reader/Readerable.jsm b/toolkit/components/reader/Readerable.jsm
new file mode 100644
index 000000000000..2268487e4296
--- /dev/null
+++ b/toolkit/components/reader/Readerable.jsm
@@ -0,0 +1,10 @@
+// -*- indent-tabs-mode: nil; js-indent-level: 2 -*-
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+var EXPORTED_SYMBOLS = ["Readerable"];
+
+#include Readability-readerable.js
+#include Readerable.js
diff --git a/toolkit/components/reader/moz.build b/toolkit/components/reader/moz.build
index 6863d6542747..c2364ce8deb4 100644
--- a/toolkit/components/reader/moz.build
+++ b/toolkit/components/reader/moz.build
@@ -8,14 +8,18 @@ JAR_MANIFESTS += ['jar.mn']
 
 EXTRA_JS_MODULES += [
   'AboutReader.jsm',
-  'ReaderMode.jsm'
+  'ReaderMode.jsm',
+]
+
+EXTRA_PP_JS_MODULES += [
+  'Readerable.jsm',
 ]
 
 EXTRA_JS_MODULES.reader = [
   'JSDOMParser.js',
   'Readability.js',
   'ReaderWorker.js',
-  'ReaderWorker.jsm'
+  'ReaderWorker.jsm',
 ]
 
 BROWSER_CHROME_MANIFESTS += [