--- a/browser/base/content/test/static/browser_all_files_referenced.js
+++ b/browser/base/content/test/static/browser_all_files_referenced.js
@@ -171,17 +171,16 @@ var whitelist = [
   // Bug 1351079
   {file: "resource://gre/modules/ISO8601DateUtils.jsm"},
   // Bug 1337345
   {file: "resource://gre/modules/Manifest.jsm"},
   // Bug 1351097
   {file: "resource://gre/modules/accessibility/AccessFu.jsm"},
   // Bug 1351637
   {file: "resource://gre/modules/sdk/bootstrap.js"},
-
 ];
 
 whitelist = new Set(whitelist.filter(item =>
   ("isFromDevTools" in item) == isDevtools &&
   (!item.skipNightly || !AppConstants.NIGHTLY_BUILD) &&
   (!item.platforms || item.platforms.includes(AppConstants.platform))
 ).map(item => item.file));
 
@@ -473,17 +472,18 @@ function findChromeUrlsFromArray(array, 
                        array.indexOf("#".charCodeAt(0), index));
     let string = "";
     for ( ; index < end; ++index) {
       string += String.fromCharCode(array[index]);
     }
 
     // Only keep strings that look like real chrome or resource urls.
     if (/chrome:\/\/[a-zA-Z09 -]+\/(content|skin|locale)\//.test(string) ||
-        /resource:\/\/gre.*\.[a-z]+/.test(string))
+        /resource:\/\/gre.*\.[a-z]+/.test(string) ||
+        string.startsWith("resource://content-accessible/"))
       gReferencesFromCode.add(string);
   }
 }
 
 add_task(async function checkAllTheFiles() {
   let libxulPath = OS.Constants.Path.libxul;
   if (AppConstants.platform != "macosx")
     libxulPath = OS.Constants.Path.libDir + "/" + libxulPath;
@@ -535,16 +535,18 @@ add_task(async function checkAllTheFiles
   // Wait for all the files to have actually loaded:
   await Promise.all(allPromises);
 
   // Keep only chrome:// files, and filter out either the devtools paths or
   // the non-devtools paths:
   let devtoolsPrefixes = ["chrome://webide/",
                           "chrome://devtools",
                           "resource://devtools/",
+                          "resource://devtools-client-jsonview/",
+                          "resource://devtools-client-shared/",
                           "resource://app/modules/devtools",
                           "resource://gre/modules/devtools"];
   let chromeFiles = [];
   for (let uri of uris) {
     uri = convertToCodeURI(uri.spec);
     if ((uri.startsWith("chrome://") || uri.startsWith("resource://")) &&
         isDevtools == devtoolsPrefixes.some(prefix => uri.startsWith(prefix)))
       chromeFiles.push(uri);

--- a/browser/base/content/test/static/browser_parsable_css.js
+++ b/browser/base/content/test/static/browser_parsable_css.js
@@ -12,17 +12,17 @@
 let whitelist = [
   // CodeMirror is imported as-is, see bug 1004423.
   {sourceName: /codemirror\.css$/i,
    isFromDevTools: true},
   // The debugger uses cross-browser CSS.
   {sourceName: /devtools\/client\/debugger\/new\/debugger.css/i,
    isFromDevTools: true},
    // Reps uses cross-browser CSS.
-   {sourceName: /devtools\/client\/shared\/components\/reps\/reps.css/i,
+   {sourceName: /devtools-client-shared\/components\/reps\/reps.css/i,
    isFromDevTools: true},
   // PDFjs is futureproofing its pseudoselectors, and those rules are dropped.
   {sourceName: /web\/viewer\.css$/i,
    errorMessage: /Unknown pseudo-class.*(fullscreen|selection)/i,
    isFromDevTools: false},
   // PDFjs rules needed for compat with other UAs.
   {sourceName: /web\/viewer\.css$/i,
    errorMessage: /Unknown property.*appearance/i,
@@ -283,51 +283,59 @@ add_task(async function checkAllTheCSS()
       manifestPromises.push(parseManifest(uri));
       return false;
     }
     return true;
   });
   // Wait for all manifest to be parsed
   await Promise.all(manifestPromises);
 
-  // We build a list of promises that get resolved when their respective
-  // files have loaded and produced no errors.
-  let allPromises = [];
-
   // filter out either the devtools paths or the non-devtools paths:
   let isDevtools = SimpleTest.harnessParameters.subsuite == "devtools";
   let devtoolsPathBits = ["webide", "devtools"];
   uris = uris.filter(uri => isDevtools == devtoolsPathBits.some(path => uri.spec.includes(path)));
 
-  for (let uri of uris) {
-    let linkEl = doc.createElement("link");
+  let loadCSS = chromeUri => new Promise(resolve => {
+    let linkEl, onLoad, onError;
+    onLoad = e => {
+      processCSSRules(linkEl.sheet);
+      resolve();
+      linkEl.removeEventListener("load", onLoad);
+      linkEl.removeEventListener("error", onError);
+    };
+    onError = e => {
+      ok(false, "Loading " + linkEl.getAttribute("href") + " threw an error!");
+      resolve();
+      linkEl.removeEventListener("load", onLoad);
+      linkEl.removeEventListener("error", onError);
+    };
+    linkEl = doc.createElement("link");
     linkEl.setAttribute("rel", "stylesheet");
-    allPromises.push(new Promise(resolve => {
-      let onLoad = (e) => {
-        processCSSRules(linkEl.sheet);
-        resolve();
-        linkEl.removeEventListener("load", onLoad);
-        linkEl.removeEventListener("error", onError);
-      };
-      let onError = (e) => {
-        ok(false, "Loading " + linkEl.getAttribute("href") + " threw an error!");
-        resolve();
-        linkEl.removeEventListener("load", onLoad);
-        linkEl.removeEventListener("error", onError);
-      };
-      linkEl.addEventListener("load", onLoad);
-      linkEl.addEventListener("error", onError);
-      linkEl.setAttribute("type", "text/css");
-      let chromeUri = convertToCodeURI(uri.spec);
-      linkEl.setAttribute("href", chromeUri + kPathSuffix);
-    }));
+    linkEl.setAttribute("type", "text/css");
+    linkEl.addEventListener("load", onLoad);
+    linkEl.addEventListener("error", onError);
+    linkEl.setAttribute("href", chromeUri + kPathSuffix);
     doc.head.appendChild(linkEl);
+  });
+
+  // We build a list of promises that get resolved when their respective
+  // files have loaded and produced no errors.
+  const kInContentCommonCSS = "chrome://global/skin/in-content/common.css";
+  let allPromises = uris.map((uri) => convertToCodeURI(uri.spec))
+                    .filter((uri) => uri !== kInContentCommonCSS);
+
+  // Make sure chrome://global/skin/in-content/common.css is loaded before other
+  // stylesheets in order to guarantee the --in-content variables can be
+  // correctly referenced.
+  if (allPromises.length !== uris.length) {
+    await loadCSS(kInContentCommonCSS);
   }
 
   // Wait for all the files to have actually loaded:
+  allPromises = allPromises.map(loadCSS);
   await Promise.all(allPromises);
 
   // Check if all the files referenced from CSS actually exist.
   for (let [image, references] of imageURIsToReferencesMap) {
     if (!chromeFileExists(image)) {
       for (let ref of references) {
         let ignored = false;
         for (let item of allowedImageReferences) {

--- a/caps/tests/mochitest/test_bug292789.html
+++ b/caps/tests/mochitest/test_bug292789.html
@@ -95,13 +95,18 @@ function loadImage(uri, expect, callback
     img.onload = success;
     img.expected = expect;
     img.callback = callback;
     img.src = uri;
     // document.getElementById("content").appendChild(img);
 }
 
 // Start off the script src test, and have it start the img tests when complete.
-testScriptSrc(runImgTest);
+// Temporarily allow content to access all resource:// URIs.
+SpecialPowers.pushPrefEnv({
+  set: [
+    ["security.all_resource_uri_content_accessible", true]
+  ]
+}, () => testScriptSrc(runImgTest));
 </script>
 </pre>
 </body>
 </html>

--- a/devtools/shared/platform/content/test/test_clipboard.html
+++ b/devtools/shared/platform/content/test/test_clipboard.html
@@ -10,32 +10,47 @@ https://bugzilla.mozilla.org/show_bug.cg
   <link rel="stylesheet" type="text/css"
         href="chrome://mochikit/content/tests/SimpleTest/test.css">
   <script type="text/javascript" src="/tests/SimpleTest/EventUtils.js"></script>
 
 <script type="application/javascript">
 "use strict";
 var exports = {}
 </script>
-
-  <script type="application/javascript"
-	  src="resource://devtools/shared/platform/content/clipboard.js"></script>
-
 </head>
-<body onload="do_tests()">
+<body onload="pre_do_tests()">
 <script type="application/javascript">
 "use strict";
 
 const RESULT = "lark bunting";
 
 function doCopy(e) {
   console.log(e.isTrusted);
   copyString(RESULT);
 }
 
+async function pre_do_tests() {
+  // Temporarily allow content to access all resource:// URIs.
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["security.all_resource_uri_content_accessible", true]
+    ]
+  });
+
+  // Load script.
+  await (() => new Promise((resolve) => {
+    var script = document.createElement("script");
+    script.onload = resolve;
+    script.src = "resource://devtools/shared/platform/content/clipboard.js";
+    document.head.appendChild(script);
+  }))();
+
+  do_tests();
+}
+
 function do_tests() {
   let elt = document.querySelector("#key");
   elt.addEventListener("keydown", doCopy);
 
   // Set the clipboard to something other than what we expect.
   SpecialPowers.clipboardCopyString("snowy owl");
 
   elt.focus();

--- a/dom/security/test/mixedcontentblocker/test_bug803225.html
+++ b/dom/security/test/mixedcontentblocker/test_bug803225.html
@@ -14,18 +14,21 @@ https://bugzilla.mozilla.org/show_bug.cg
   var counter = 0;
   var settings = [ [true, true], [true, false], [false, true], [false, false] ];
 
   var blockActive;
   var blockDisplay;
 
   //Cycle through 4 different preference settings.
   function changePrefs(callback) {
-    let newPrefs = [["security.mixed_content.block_display_content", settings[counter][0]],
-                    ["security.mixed_content.block_active_content", settings[counter][1]]];
+    let newPrefs = [
+      ["security.all_resource_uri_content_accessible", true], // Temporarily allow content to access all resource:// URIs.
+      ["security.mixed_content.block_display_content", settings[counter][0]],
+      ["security.mixed_content.block_active_content", settings[counter][1]]
+    ];
 
     SpecialPowers.pushPrefEnv({"set": newPrefs}, function () {
       blockDisplay = SpecialPowers.getBoolPref("security.mixed_content.block_display_content");
       blockActive = SpecialPowers.getBoolPref("security.mixed_content.block_active_content");
       counter++;
       callback();
     });
   }

--- a/parser/htmlparser/tests/reftest/bug482921-1-ref.html
+++ b/parser/htmlparser/tests/reftest/bug482921-1-ref.html
@@ -1,9 +1,9 @@
-<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://gre-resources/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="doctype">&lt;!DOCTYPE html&gt;</span>
+<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://content-accessible/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="doctype">&lt;!DOCTYPE html&gt;</span>
 <span id></span><span>&lt;<span class="start-tag">html</span>&gt;</span>
 <span id></span><span>&lt;<span class="start-tag">head</span>&gt;</span>
 <span id></span><span>&lt;<span class="start-tag">title</span>&gt;</span><span>Title</span><span>&lt;/<span class="end-tag">title</span>&gt;</span>
 <span id></span><span>&lt;<span class="start-tag">script</span>&gt;</span>
 <span id></span>var lt = "&lt;";
 <span id></span>&lt;!--
 <span id></span>var s = "&lt;script&gt;foo&lt;/script&gt;";
 <span id></span>--&gt;

--- a/parser/htmlparser/tests/reftest/bug482921-2-ref.html
+++ b/parser/htmlparser/tests/reftest/bug482921-2-ref.html
@@ -1,9 +1,9 @@
-<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://gre-resources/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="pi">&lt;?xml version="1.0" encoding="utf-8"?&gt;</span>
+<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://content-accessible/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="pi">&lt;?xml version="1.0" encoding="utf-8"?&gt;</span>
 <span id></span><span class="pi">&lt;?foo bar?&gt;</span>
 <span id></span><span>&lt;<span class="start-tag">html</span>&gt;</span>
 <span id></span><span>&lt;<span class="start-tag">head</span>&gt;</span>
 <span id></span><span>&lt;<span class="start-tag">title</span>&gt;</span><span>Title</span><span>&lt;/<span class="end-tag">title</span>&gt;</span>
 <span id></span><span>&lt;<span class="start-tag">script</span>&gt;</span>
 <span id></span>var s = "<span>&lt;<span class="start-tag">script</span>&gt;</span><span>foo</span><span>&lt;/<span class="end-tag">script</span>&gt;</span>";
 <span id></span><span class="comment">&lt;!--
 <span id></span>var s = "&lt;script&gt;foo&lt;/script&gt;";

--- a/parser/htmlparser/tests/reftest/bug535530-2-ref.html
+++ b/parser/htmlparser/tests/reftest/bug535530-2-ref.html
@@ -1,9 +1,9 @@
-<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://gre-resources/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="doctype">&lt;!DOCTYPE html&gt;</span>
+<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://content-accessible/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="doctype">&lt;!DOCTYPE html&gt;</span>
 <span id></span>XX<span class="error">&amp;</span>XX
 <span id></span>XX<span class="error">&amp;</span>nXX
 <span id></span>XX<span class="error">&amp;</span>noXX
 <span id></span>XX<span class="error entity">&amp;not</span>XX
 <span id></span>XX<span class="error entity">&amp;noti</span>XX
 <span id></span>XX<span class="error entity">&amp;notin</span>XX
 <span id></span>XX<span class="error">&amp;</span>;XX
 <span id></span>XX<span class="error">&amp;</span>n;XX

--- a/parser/htmlparser/tests/reftest/bug704667-1-ref.html
+++ b/parser/htmlparser/tests/reftest/bug704667-1-ref.html
@@ -1,4 +1,4 @@
-<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://gre-resources/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="error comment">&lt;!--&gt;</span> <span class="error comment">&lt;!X&gt;</span>
+<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://content-accessible/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="error comment">&lt;!--&gt;</span> <span class="error comment">&lt;!X&gt;</span>
 <span id></span>
 </pre>
 <!-- View source CSS matches the <pre id> and <span id> elements and produces line numbers. -->

--- a/parser/htmlparser/tests/reftest/bug731234-1-ref.html
+++ b/parser/htmlparser/tests/reftest/bug731234-1-ref.html
@@ -1,9 +1,9 @@
-<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://gre-resources/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="doctype">&lt;!DOCTYPE html&gt;</span><span>
+<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://content-accessible/viewsource.css"></head><body id="viewsource" class="wrap highlight"><pre id><span class="doctype">&lt;!DOCTYPE html&gt;</span><span>
 <span id></span></span><span>&lt;<span class="start-tag">body</span>&gt;</span><span>
 <span id></span></span><span>&lt;<span class="start-tag">script</span>&gt;</span><span></span><span>&lt;/<span class="end-tag">script</span>&gt;</span><span>X
 <span id></span></span><span>&lt;<span class="start-tag">script</span>&gt;</span><span></span><span>&lt;/<span class="end-tag">script</span> &gt;</span><span>X
 <span id></span></span><span>&lt;<span class="start-tag">script</span>&gt;</span><span></span><span>&lt;/<span class="end-tag">script</span>
 <span id></span>&gt;</span><span>X
 <span id></span></span><span>&lt;<span class="start-tag">script</span>&gt;</span><span></span><span title="End tag had attributes." class="error">&lt;/<span class="end-tag">script</span> <span class="attribute-name">foo</span>&gt;</span><span>X
 <span id></span></span><span>&lt;<span class="start-tag">script</span>&gt;</span><span></span><span title="End tag had attributes." class="error">&lt;/<span class="end-tag">script</span> <span class="attribute-name">foo</span>=<a class="attribute-value">bar</a>&gt;</span><span>X
 <span id></span></span><span>&lt;<span class="start-tag">script</span>&gt;</span><span></span><span title="End tag had attributes." class="error">&lt;/<span class="end-tag">script</span> <span class="attribute-name">foo</span>="<a class="attribute-value">bar</a>"&gt;</span><span>X

--- a/parser/htmlparser/tests/reftest/bug910588-1-ref.html
+++ b/parser/htmlparser/tests/reftest/bug910588-1-ref.html
@@ -1,2 +1,2 @@
-<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://gre-resources/viewsource.css"></head><body id="viewsource" class="highlight" style="-moz-tab-size: 4"><pre id="line1"><span></span><span class="doctype">&lt;!DOCTYPE html&gt;</span><span></span><span>&lt;<span class="start-tag">table</span>&gt;</span><span></span><span title="Start tag “input” seen in “table”." class="error">&lt;<span class="start-tag">input</span> <span class="attribute-name">type</span>=<a class="attribute-value">hidden</a>&gt;</span><span></span><span>&lt;/<span class="end-tag">table</span>&gt;</span><span>
+<!DOCTYPE html><html><head><title></title><link rel="stylesheet" type="text/css" href="resource://content-accessible/viewsource.css"></head><body id="viewsource" class="highlight" style="-moz-tab-size: 4"><pre id="line1"><span></span><span class="doctype">&lt;!DOCTYPE html&gt;</span><span></span><span>&lt;<span class="start-tag">table</span>&gt;</span><span></span><span title="Start tag “input” seen in “table”." class="error">&lt;<span class="start-tag">input</span> <span class="attribute-name">type</span>=<a class="attribute-value">hidden</a>&gt;</span><span></span><span>&lt;/<span class="end-tag">table</span>&gt;</span><span>
 <span id="line2"></span></span></pre></body></html>