--- a/toolkit/components/extensions/ExtensionContent.jsm
+++ b/toolkit/components/extensions/ExtensionContent.jsm
@@ -96,17 +96,16 @@ var apiManager = new class extends Schem
 // Represents a content script.
 function Script(extension, options, deferred = PromiseUtils.defer()) {
   this.extension = extension;
   this.options = options;
   this.run_at = this.options.run_at;
   this.js = this.options.js || [];
   this.css = this.options.css || [];
   this.remove_css = this.options.remove_css;
-  this.match_about_blank = this.options.match_about_blank;
 
   this.deferred = deferred;
 
   this.matches_ = new MatchPattern(this.options.matches);
   this.exclude_matches_ = new MatchPattern(this.options.exclude_matches || null);
   // TODO: MatchPattern should pre-mangle host-only patterns so that we
   // don't need to call a separate match function.
   this.matches_host_ = new MatchPattern(this.options.matchesHost || null);
@@ -136,22 +135,16 @@ Script.prototype = {
     let uri = window.document.documentURIObject;
 
     // If mozAddonManager is present on this page, don't allow
     // content scripts.
     if (window.navigator.mozAddonManager !== undefined) {
       return false;
     }
 
-    if (this.match_about_blank && ["about:blank", "about:srcdoc"].includes(uri.spec)) {
-      // When matching about:blank/srcdoc documents, the checks below
-      // need to be performed against the "owner" document's URI.
-      uri = window.document.nodePrincipal.URI;
-    }
-
     if (!(this.matches_.matches(uri) || this.matches_host_.matchesIgnoringPath(uri))) {
       return false;
     }
 
     if (this.exclude_matches_.matches(uri)) {
       return false;
     }
 
@@ -168,16 +161,18 @@ Script.prototype = {
     if (this.options.frame_id != null) {
       if (WebNavigationFrames.getFrameId(window) != this.options.frame_id) {
         return false;
       }
     } else if (!this.options.all_frames && window.top != window) {
       return false;
     }
 
+    // TODO: match_about_blank.
+
     return true;
   },
 
   cleanup(window) {
     if (!this.remove_css) {
       let winUtils = window.QueryInterface(Ci.nsIInterfaceRequestor)
                            .getInterface(Ci.nsIDOMWindowUtils);
 
@@ -426,60 +421,44 @@ DocumentManager = {
 
   // Map[windowId -> Map[extensionId -> ExtensionContext]]
   contentScriptWindows: new Map(),
 
   // Map[windowId -> ExtensionContext]
   extensionPageWindows: new Map(),
 
   init() {
-    Services.obs.addObserver(this, "content-document-global-created", false);
     Services.obs.addObserver(this, "document-element-inserted", false);
     Services.obs.addObserver(this, "inner-window-destroyed", false);
   },
 
   uninit() {
-    Services.obs.removeObserver(this, "content-document-global-created");
     Services.obs.removeObserver(this, "document-element-inserted");
     Services.obs.removeObserver(this, "inner-window-destroyed");
   },
 
   getWindowState(contentWindow) {
     let readyState = contentWindow.document.readyState;
     if (readyState == "complete") {
       return "document_idle";
     }
     if (readyState == "interactive") {
       return "document_end";
     }
     return "document_start";
   },
 
   observe: function(subject, topic, data) {
-    // For some types of documents (about:blank), we only see the first
-    // notification, for others (data: URIs) we only observe the second.
-    if (topic == "content-document-global-created" || topic == "document-element-inserted") {
+    if (topic == "document-element-inserted") {
       let document = subject;
       let window = document && document.defaultView;
-
-      if (topic == "content-document-global-created") {
-        window = subject;
-        document = window && window.document;
-      }
-
       if (!document || !document.location || !window) {
         return;
       }
 
-      // Make sure we always load exactly once (notice != used as logical XOR),
-      // usually on document-element-inserted, except for about:blank documents.
-      if ((topic == "content-document-global-created") != (window.location.href == "about:blank")) {
-        return;
-      }
-
       // Make sure we only load into frames that ExtensionContent.init
       // was called on (i.e., not frames for social or sidebars).
       let mm = getWindowMessageManager(window);
       if (!mm || !ExtensionContent.globals.has(mm)) {
         return;
       }
 
       // Enable the content script APIs should be available in subframes' window
@@ -498,18 +477,17 @@ DocumentManager = {
           if (apiLevel == CONTENTSCRIPT_PRIVILEGES) {
             DocumentManager.getExtensionPageContext(extension, window);
           } else if (apiLevel == FULL_PRIVILEGES) {
             ExtensionChild.createExtensionContext(extension, window);
           }
         }
       }
 
-      this.trigger(window);
-
+      this.trigger("document_start", window);
       /* eslint-disable mozilla/balanced-listeners */
       window.addEventListener("DOMContentLoaded", this, true);
       window.addEventListener("load", this, true);
       /* eslint-enable mozilla/balanced-listeners */
     } else if (topic == "inner-window-destroyed") {
       let windowId = subject.QueryInterface(Ci.nsISupportsPRUint64).data;
 
       MessageChannel.abortResponses({innerWindowID: windowId});
@@ -543,19 +521,19 @@ DocumentManager = {
       // listening on.
       return;
     }
     window.removeEventListener(event.type, this, true);
 
     // Need to check if we're still on the right page? Greasemonkey does this.
 
     if (event.type == "DOMContentLoaded") {
-      this.trigger(window);
+      this.trigger("document_end", window);
     } else if (event.type == "load") {
-      this.trigger(window);
+      this.trigger("document_idle", window);
     }
   },
 
   // Used to executeScript, insertCSS and removeCSS.
   executeScript(global, extensionId, options) {
     let extension = ExtensionManager.get(extensionId);
 
     let executeInWin = (window) => {
@@ -683,17 +661,17 @@ DocumentManager = {
     MessageChannel.abortResponses({extensionId});
 
     this.extensionCount--;
     if (this.extensionCount == 0) {
       this.uninit();
     }
   },
 
-  trigger(window) {
+  trigger(when, window) {
     let state = this.getWindowState(window);
 
     if (state == "document_start") {
       for (let extension of ExtensionManager.extensions.values()) {
         for (let script of extension.scripts) {
           if (script.matches(window)) {
             let context = this.getContentScriptContext(extension, window);
             context.addScript(script);

deleted file mode 100644
--- a/toolkit/components/extensions/test/mochitest/file_with_about_blank.html
+++ /dev/null
@@ -1,10 +0,0 @@
-<!doctype html>
-<html>
-<head>
-  <meta charset="utf-8">
-</head>
-<body>
-  <iframe id="a_b" src="about:blank"></iframe>
-  <iframe srcdoc="galactica actual" src="adama"></iframe>
-</body>
-</html>

--- a/toolkit/components/extensions/test/mochitest/mochitest.ini
+++ b/toolkit/components/extensions/test/mochitest/mochitest.ini
@@ -13,17 +13,16 @@ support-files =
   file_webNavigation_frameClientRedirect.html
   file_webNavigation_frameRedirect.html
   file_webNavigation_manualSubframe.html
   file_webNavigation_manualSubframe_page1.html
   file_webNavigation_manualSubframe_page2.html
   file_WebNavigation_page1.html
   file_WebNavigation_page2.html
   file_WebNavigation_page3.html
-  file_with_about_blank.html
   file_image_good.png
   file_image_bad.png
   file_image_redirect.png
   file_style_good.css
   file_style_bad.css
   file_style_redirect.css
   file_script_good.js
   file_script_bad.js
@@ -46,18 +45,16 @@ skip-if = os == 'android' # Android does
 [test_ext_content_security_policy.html]
 [test_ext_contentscript.html]
 [test_ext_contentscript_api_injection.html]
 [test_ext_contentscript_context.html]
 [test_ext_contentscript_create_iframe.html]
 [test_ext_contentscript_devtools_metadata.html]
 [test_ext_contentscript_exporthelpers.html]
 [test_ext_contentscript_css.html]
-[test_ext_contentscript_about_blank.html]
-skip-if = (os == 'android') # bug 1312357
 [test_ext_contentscript_teardown.html]
 skip-if = (os == 'android') # Android does not support tabs API. Bug 1260250
 [test_ext_exclude_include_globs.html]
 [test_ext_i18n_css.html]
 [test_ext_generate.html]
 [test_ext_notifications.html]
 [test_ext_permission_xhr.html]
 [test_ext_runtime_connect.html]

deleted file mode 100644
--- a/toolkit/components/extensions/test/mochitest/test_ext_contentscript_about_blank.html
+++ /dev/null
@@ -1,117 +0,0 @@
-<!doctype html>
-<html>
-<head>
-  <title>Test content script match_about_blank option</title>
-  <script type="text/javascript" src="/tests/SimpleTest/SpawnTask.js"></script>
-  <script type="text/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
-  <script type="text/javascript" src="/tests/SimpleTest/ExtensionTestUtils.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
-</head>
-<body>
-
-<script type="text/javascript">
-"use strict";
-
-add_task(function* test_contentscript_about_blank() {
-  const manifest = {
-    content_scripts: [
-      {
-        match_about_blank: true,
-        matches: ["http://mochi.test/*/file_with_about_blank.html", "http://example.com/*"],
-        all_frames: true,
-        css: ["all.css"],
-        js: ["all.js"],
-      }, {
-        matches: ["http://mochi.test/*/file_with_about_blank.html"],
-        css: ["mochi_without.css"],
-        js: ["mochi_without.js"],
-        all_frames: true,
-      }, {
-        match_about_blank: true,
-        matches: ["http://mochi.test/*/file_with_about_blank.html"],
-        css: ["mochi_with.css"],
-        js: ["mochi_with.js"],
-        all_frames: true,
-      },
-    ],
-  };
-
-  const files = {
-    "all.js": function() {
-      browser.runtime.sendMessage("all");
-    },
-    "all.css": `
-      body { color: red; }
-    `,
-    "mochi_without.js": function() {
-      browser.runtime.sendMessage("mochi_without");
-    },
-    "mochi_without.css": `
-      body { background: yellow; }
-    `,
-    "mochi_with.js": function() {
-      browser.runtime.sendMessage("mochi_with");
-    },
-    "mochi_with.css": `
-      body { text-align: right; }
-    `,
-  };
-
-  function background() {
-    browser.runtime.onMessage.addListener((script, {url}) => {
-      const kind = url.startsWith("about:") ? url : "top";
-      browser.test.sendMessage("script", [script, kind, url]);
-      browser.test.sendMessage(`${script}:${kind}`);
-    });
-  }
-
-  const PATH = "tests/toolkit/components/extensions/test/mochitest/file_with_about_blank.html";
-  const extension = ExtensionTestUtils.loadExtension({manifest, files, background});
-  yield extension.startup();
-
-  let count = 0;
-  extension.onMessage("script", script => {
-    info(`script ran: ${script}`);
-    count++;
-  });
-
-  let win = window.open("http://example.com/" + PATH);
-  yield Promise.all([
-    extension.awaitMessage("all:top"),
-    extension.awaitMessage("all:about:blank"),
-    extension.awaitMessage("all:about:srcdoc"),
-  ]);
-  is(count, 3, "exactly 3 scripts ran");
-  win.close();
-
-  win = window.open("http://mochi.test:8888/" + PATH);
-  yield Promise.all([
-    extension.awaitMessage("all:top"),
-    extension.awaitMessage("all:about:blank"),
-    extension.awaitMessage("all:about:srcdoc"),
-    extension.awaitMessage("mochi_without:top"),
-    extension.awaitMessage("mochi_with:top"),
-    extension.awaitMessage("mochi_with:about:blank"),
-    extension.awaitMessage("mochi_with:about:srcdoc"),
-  ]);
-
-  let style = win.getComputedStyle(win.document.body);
-  is(style.color, "rgb(255, 0, 0)", "top window text color is red");
-  is(style.backgroundColor, "rgb(255, 255, 0)", "top window background is yellow");
-  is(style.textAlign, "right", "top window text is right-aligned");
-
-  let a_b = win.document.getElementById("a_b");
-  style = a_b.contentWindow.getComputedStyle(a_b.contentDocument.body);
-  is(style.color, "rgb(255, 0, 0)", "about:blank iframe text color is red");
-  is(style.backgroundColor, "transparent", "about:blank iframe background is transparent");
-  is(style.textAlign, "right", "about:blank text is right-aligned");
-
-  is(count, 10, "exactly 7 more scripts ran");
-  win.close();
-
-  yield extension.unload();
-});
-</script>
-
-</body>
-</html>