diff --git a/browser/base/content/test/general/browser.ini b/browser/base/content/test/general/browser.ini
index c1ac21a487ff..07ab48415753 100644
--- a/browser/base/content/test/general/browser.ini
+++ b/browser/base/content/test/general/browser.ini
@@ -32,6 +32,8 @@ support-files =
   ctxmenu-image.png
   discovery.html
   download_page.html
+  download_page_1.txt
+  download_page_2.txt
   dummy_page.html
   feed_tab.html
   file_generic_favicon.ico
diff --git a/browser/base/content/test/general/browser_bug575561.js b/browser/base/content/test/general/browser_bug575561.js
index a769d1a2bd50..9837aa3baded 100644
--- a/browser/base/content/test/general/browser_bug575561.js
+++ b/browser/base/content/test/general/browser_bug575561.js
@@ -5,6 +5,11 @@ const TEST_URL = "http://example.com/browser/browser/base/content/test/general/a
 add_task(async function() {
   SimpleTest.requestCompleteLog();
 
+  // allow top level data: URI navigations, otherwise clicking data: link fails
+  await SpecialPowers.pushPrefEnv({
+    "set": [["security.data_uri.block_toplevel_data_uri_navigations", false]]
+  });
+
   // Pinned: Link to the same domain should not open a new tab
   // Tests link to http://example.com/browser/browser/base/content/test/general/dummy_page.html
   await testLink(0, true, false);
diff --git a/browser/base/content/test/general/browser_bug734076.js b/browser/base/content/test/general/browser_bug734076.js
index 45ad6a8dffe2..fdfa13db2796 100644
--- a/browser/base/content/test/general/browser_bug734076.js
+++ b/browser/base/content/test/general/browser_bug734076.js
@@ -2,6 +2,13 @@
  * http://creativecommons.org/publicdomain/zero/1.0/ */
 
 add_task(async function() {
+
+  // allow top level data: URI navigations, otherwise loading data: URIs
+  // in toplevel windows fail.
+  await SpecialPowers.pushPrefEnv({
+    "set": [["security.data_uri.block_toplevel_data_uri_navigations", false]]
+  });
+
   let tab = await BrowserTestUtils.openNewForegroundTab(gBrowser, null, false);
 
   let browser = tab.linkedBrowser;
diff --git a/browser/base/content/test/general/browser_fullscreen-window-open.js b/browser/base/content/test/general/browser_fullscreen-window-open.js
index 10457a698849..3896dc21bf70 100644
--- a/browser/base/content/test/general/browser_fullscreen-window-open.js
+++ b/browser/base/content/test/general/browser_fullscreen-window-open.js
@@ -6,6 +6,7 @@ var Cc = Components.classes;
 var Ci = Components.interfaces;
 
 const PREF_DISABLE_OPEN_NEW_WINDOW = "browser.link.open_newwindow.disabled_in_fullscreen";
+const PREF_BLOCK_TOPLEVEL_DATA = "security.data_uri.block_toplevel_data_uri_navigations";
 const isOSX = (Services.appinfo.OS === "Darwin");
 
 const TEST_FILE = "file_fullscreen-window-open.html";
@@ -19,6 +20,7 @@ async function test() {
   waitForExplicitFinish();
 
   Services.prefs.setBoolPref(PREF_DISABLE_OPEN_NEW_WINDOW, true);
+  Services.prefs.setBoolPref(PREF_BLOCK_TOPLEVEL_DATA, false);
 
   newWin = await BrowserTestUtils.openNewBrowserWindow();
   newBrowser = newWin.gBrowser;
@@ -37,6 +39,7 @@ registerCleanupFunction(async function() {
   await BrowserTestUtils.closeWindow(newWin);
 
   Services.prefs.clearUserPref(PREF_DISABLE_OPEN_NEW_WINDOW);
+  Services.prefs.clearUserPref(PREF_BLOCK_TOPLEVEL_DATA);
 });
 
 var gTests = [
diff --git a/browser/base/content/test/general/download_page.html b/browser/base/content/test/general/download_page.html
index 3093ffa2e2cb..a7664e1b2599 100644
--- a/browser/base/content/test/general/download_page.html
+++ b/browser/base/content/test/general/download_page.html
@@ -11,13 +11,13 @@ https://bugzilla.mozilla.org/show_bug.cgi?id=676619
     <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=676619">Bug 676619</a>
     <br/>
     <ul>
-        <li><a href="data:text/plain,Hey What are you looking for?"
+        <li><a href="download_page_1.txt"
                 download="test.txt" id="link1">Download "test.txt"</a></li>
         <li><a href="video.ogg"
                 download id="link2">Download "video.ogg"</a></li>
         <li><a href="video.ogg"
                 download="just some video" id="link3">Download "just some video"</a></li>
-        <li><a href="data:text/plain,test"
+        <li><a href="download_page_2.txt"
                 download="with-target.txt" id="link4">Download "with-target.txt"</a></li>
         <li><a href="javascript:(1+2)+''"
             download="javascript.txt" id="link5">Download "javascript.txt"</a></li>
diff --git a/browser/base/content/test/general/download_page_1.txt b/browser/base/content/test/general/download_page_1.txt
new file mode 100644
index 000000000000..404b2da2ad0e
--- /dev/null
+++ b/browser/base/content/test/general/download_page_1.txt
@@ -0,0 +1 @@
+Hey What are you looking for?
diff --git a/browser/base/content/test/general/download_page_2.txt b/browser/base/content/test/general/download_page_2.txt
new file mode 100644
index 000000000000..9daeafb9864c
--- /dev/null
+++ b/browser/base/content/test/general/download_page_2.txt
@@ -0,0 +1 @@
+test
diff --git a/browser/base/content/test/popups/browser.ini b/browser/base/content/test/popups/browser.ini
index 01f00318f8aa..279dfc69882e 100644
--- a/browser/base/content/test/popups/browser.ini
+++ b/browser/base/content/test/popups/browser.ini
@@ -1,6 +1,12 @@
 [browser_popupUI.js]
 [browser_popup_blocker.js]
-support-files = popup_blocker.html
+support-files =
+  popup_blocker.html
+  popup_blocker_a.html
+  popup_blocker_b.html
 skip-if = (os == 'linux') || (e10s && debug) # Frequent bug 1081925 and bug 1125520 failures
 [browser_popup_frames.js]
-support-files = popup_blocker.html
+support-files =
+  popup_blocker.html
+  popup_blocker_a.html
+  popup_blocker_b.html
diff --git a/browser/base/content/test/popups/browser_popup_blocker.js b/browser/base/content/test/popups/browser_popup_blocker.js
index e4473b265d4a..68839db71732 100644
--- a/browser/base/content/test/popups/browser_popup_blocker.js
+++ b/browser/base/content/test/popups/browser_popup_blocker.js
@@ -64,8 +64,8 @@ add_task(async function test_opening_blocked_popups() {
 
   gBrowser.tabContainer.removeEventListener("TabOpen", onTabOpen);
 
-  is(popupTabs[0].linkedBrowser.currentURI.spec, "data:text/plain;charset=utf-8,a", "Popup a");
-  is(popupTabs[1].linkedBrowser.currentURI.spec, "data:text/plain;charset=utf-8,b", "Popup b");
+  ok(popupTabs[0].linkedBrowser.currentURI.spec.endsWith("popup_blocker_a.html"), "Popup a");
+  ok(popupTabs[1].linkedBrowser.currentURI.spec.endsWith("popup_blocker_b.html"), "Popup b");
 
   // Clean up.
   gBrowser.removeTab(tab);
diff --git a/browser/base/content/test/popups/popup_blocker.html b/browser/base/content/test/popups/popup_blocker.html
index 6e2b7db15536..8e2d95805928 100644
--- a/browser/base/content/test/popups/popup_blocker.html
+++ b/browser/base/content/test/popups/popup_blocker.html
@@ -6,8 +6,8 @@
   </head>
   <body>
     <script type="text/javascript">
-      window.open("data:text/plain;charset=utf-8,a", "a");
-      window.open("data:text/plain;charset=utf-8,b", "b");
+      window.open("popup_blocker_a.html", "a");
+      window.open("popup_blocker_b.html", "b");
     </script>
   </body>
 </html>
diff --git a/browser/base/content/test/popups/popup_blocker_a.html b/browser/base/content/test/popups/popup_blocker_a.html
new file mode 100644
index 000000000000..b6f94b5b2683
--- /dev/null
+++ b/browser/base/content/test/popups/popup_blocker_a.html
@@ -0,0 +1 @@
+<html><body>a</body></html>
diff --git a/browser/base/content/test/popups/popup_blocker_b.html b/browser/base/content/test/popups/popup_blocker_b.html
new file mode 100644
index 000000000000..954061e2cec1
--- /dev/null
+++ b/browser/base/content/test/popups/popup_blocker_b.html
@@ -0,0 +1 @@
+<html><body>b</body></html>
diff --git a/browser/base/content/test/urlbar/browser.ini b/browser/base/content/test/urlbar/browser.ini
index 7419a15a3f90..7ae3b0912916 100644
--- a/browser/base/content/test/urlbar/browser.ini
+++ b/browser/base/content/test/urlbar/browser.ini
@@ -29,6 +29,7 @@ support-files =
 [browser_bug556061.js]
 subsuite = clipboard
 [browser_bug562649.js]
+support-files = file_bug562649.html
 [browser_bug623155.js]
 support-files =
   redirect_bug623155.sjs
diff --git a/browser/base/content/test/urlbar/browser_bug562649.js b/browser/base/content/test/urlbar/browser_bug562649.js
index cbacd8338742..94db8226bc15 100644
--- a/browser/base/content/test/urlbar/browser_bug562649.js
+++ b/browser/base/content/test/urlbar/browser_bug562649.js
@@ -1,5 +1,6 @@
 function test() {
-  const URI = "data:text/plain,bug562649";
+  const TEST_PATH = getRootDirectory(gTestPath).replace("chrome://mochitests/content", "https://example.com");
+  const URI = TEST_PATH + "file_bug562649.html";
   window.browserDOMWindow.openURI(makeURI(URI),
                                   null,
                                   Ci.nsIBrowserDOMWindow.OPEN_NEWTAB,
diff --git a/browser/base/content/test/urlbar/file_bug562649.html b/browser/base/content/test/urlbar/file_bug562649.html
new file mode 100644
index 000000000000..a787b708984e
--- /dev/null
+++ b/browser/base/content/test/urlbar/file_bug562649.html
@@ -0,0 +1 @@
+<html><body>bug562649</body></html>
diff --git a/browser/components/extensions/test/browser/browser_ext_tabs_executeScript_bad.js b/browser/components/extensions/test/browser/browser_ext_tabs_executeScript_bad.js
index 0ec676c56139..e65c78dafc68 100644
--- a/browser/components/extensions/test/browser/browser_ext_tabs_executeScript_bad.js
+++ b/browser/components/extensions/test/browser/browser_ext_tabs_executeScript_bad.js
@@ -203,6 +203,12 @@ add_task(async function testBadPermissions() {
 });
 
 add_task(async function testMatchDataURI() {
+  // allow top level data: URI navigations, otherwise
+  // window.location.href = data: would be blocked
+  await SpecialPowers.pushPrefEnv({
+    "set": [["security.data_uri.block_toplevel_data_uri_navigations", false]],
+  });
+
   const target = ExtensionTestUtils.loadExtension({
     files: {
       "page.html": `<!DOCTYPE html>
diff --git a/browser/components/originattributes/test/browser/browser_firstPartyIsolation_aboutPages.js b/browser/components/originattributes/test/browser/browser_firstPartyIsolation_aboutPages.js
index a9148d34d53f..5534110bfa0e 100644
--- a/browser/components/originattributes/test/browser/browser_firstPartyIsolation_aboutPages.js
+++ b/browser/components/originattributes/test/browser/browser_firstPartyIsolation_aboutPages.js
@@ -68,6 +68,11 @@ function frame_script() {
  * Check if data: URI inherits firstPartyDomain from about:blank correctly.
  */
 add_task(async function test_remote_window_open_data_uri() {
+  // allow top level data: URI navigations, otherwise
+  // <a href="data:" would fail.
+  await SpecialPowers.pushPrefEnv({
+    "set": [["security.data_uri.block_toplevel_data_uri_navigations", false]]
+  });
   let win = await BrowserTestUtils.openNewBrowserWindow({ remote: true });
   let browser = win.gBrowser.selectedBrowser;
   let mm = browser.messageManager;
diff --git a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_newtab_from_popup.js b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_newtab_from_popup.js
index bf5c51de12d5..d721f0a1b82f 100644
--- a/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_newtab_from_popup.js
+++ b/browser/components/privatebrowsing/test/browser/browser_privatebrowsing_newtab_from_popup.js
@@ -22,6 +22,10 @@ const WINDOW_BODY = `data:text/html,
                      </a>`;
 
 add_task(async function test_private_popup_window_opens_private_tabs() {
+  // allow top level data: URI navigations, otherwise clicking a data: link fails
+  await SpecialPowers.pushPrefEnv({
+    "set": [["security.data_uri.block_toplevel_data_uri_navigations", false]]
+  });
   let privWin = await BrowserTestUtils.openNewBrowserWindow({ private: true });
 
   // Sanity check - this browser better be private.
diff --git a/browser/components/sessionstore/test/browser.ini b/browser/components/sessionstore/test/browser.ini
index b6bbcb062eb7..508455f62017 100644
--- a/browser/components/sessionstore/test/browser.ini
+++ b/browser/components/sessionstore/test/browser.ini
@@ -70,7 +70,9 @@ support-files =
 [browser_aboutPrivateBrowsing.js]
 [browser_aboutSessionRestore.js]
 [browser_async_duplicate_tab.js]
+support-files = file_async_duplicate_tab.html
 [browser_async_flushes.js]
+support-files = file_async_flushes.html
 run-if = e10s && crashreporter
 skip-if = debug # bug 1167933
 [browser_async_remove_tab.js]
@@ -111,6 +113,8 @@ skip-if = e10s # Bug 1271024
 [browser_scrollPositions.js]
 [browser_scrollPositionsReaderMode.js]
 [browser_sessionHistory.js]
+support-files =
+  file_sessionHistory_hashchange.html
 [browser_sessionStorage.js]
 [browser_sessionStorage_size.js]
 [browser_tab_label_during_restore.js]
diff --git a/browser/components/sessionstore/test/browser_911547.js b/browser/components/sessionstore/test/browser_911547.js
index cb95ddad7f2a..9f0cb1adc6dd 100644
--- a/browser/components/sessionstore/test/browser_911547.js
+++ b/browser/components/sessionstore/test/browser_911547.js
@@ -11,6 +11,10 @@
 //    it's enclosing context.
 
 add_task(async function test() {
+  // allow top level data: URI navigations, otherwise clicking a data: link fails
+  await SpecialPowers.pushPrefEnv({
+    "set": [["security.data_uri.block_toplevel_data_uri_navigations", false]]
+  });
   let dataURIPref = Services.prefs.getBoolPref("security.data_uri.unique_opaque_origin");
   // create a tab that has a CSP
   let testURL = "http://mochi.test:8888/browser/browser/components/sessionstore/test/browser_911547_sample.html";
diff --git a/browser/components/sessionstore/test/browser_async_duplicate_tab.js b/browser/components/sessionstore/test/browser_async_duplicate_tab.js
index f9e8e1897aa7..353bfec73621 100644
--- a/browser/components/sessionstore/test/browser_async_duplicate_tab.js
+++ b/browser/components/sessionstore/test/browser_async_duplicate_tab.js
@@ -1,6 +1,8 @@
 "use strict";
 
-const URL = "data:text/html;charset=utf-8,<a href=%23>clickme</a>";
+const PATH = getRootDirectory(gTestPath)
+             .replace("chrome://mochitests/content/", "http://example.com/");
+const URL = PATH + "file_async_duplicate_tab.html";
 
 add_task(async function test_duplicate() {
   // Create new tab.
diff --git a/browser/components/sessionstore/test/browser_async_flushes.js b/browser/components/sessionstore/test/browser_async_flushes.js
index 7951342722db..215d4354354f 100644
--- a/browser/components/sessionstore/test/browser_async_flushes.js
+++ b/browser/components/sessionstore/test/browser_async_flushes.js
@@ -1,6 +1,8 @@
 "use strict";
 
-const URL = "data:text/html;charset=utf-8,<a href=%23>clickme</a>";
+const PATH = getRootDirectory(gTestPath)
+             .replace("chrome://mochitests/content/", "http://example.com/");
+const URL = PATH + "file_async_flushes.html";
 
 add_task(async function test_flush() {
   // Create new tab.
diff --git a/browser/components/sessionstore/test/browser_dynamic_frames.js b/browser/components/sessionstore/test/browser_dynamic_frames.js
index 37149caca858..419517a546e4 100644
--- a/browser/components/sessionstore/test/browser_dynamic_frames.js
+++ b/browser/components/sessionstore/test/browser_dynamic_frames.js
@@ -8,6 +8,10 @@
  * inserted iframes are ignored.
  */
 add_task(async function() {
+  // allow top level data: URI navigations, otherwise clicking a data: link fails
+  await SpecialPowers.pushPrefEnv({
+    "set": [["security.data_uri.block_toplevel_data_uri_navigations", false]]
+  });
   // This URL has the following frames:
   //  + data:text/html,A (static)
   //  + data:text/html,B (static)
@@ -46,6 +50,10 @@ add_task(async function() {
  * create a second root entry that doesn't contain any dynamic children either.
  */
 add_task(async function() {
+  // allow top level data: URI navigations, otherwise clicking a data: link fails
+  await SpecialPowers.pushPrefEnv({
+    "set": [["security.data_uri.block_toplevel_data_uri_navigations", false]]
+  });
   // This URL has the following frames:
   //  + data:text/html,A (static)
   //  + data:text/html,C (dynamic iframe)
diff --git a/browser/components/sessionstore/test/browser_sessionHistory.js b/browser/components/sessionstore/test/browser_sessionHistory.js
index 20196fdc037b..4074e52870fd 100644
--- a/browser/components/sessionstore/test/browser_sessionHistory.js
+++ b/browser/components/sessionstore/test/browser_sessionHistory.js
@@ -37,8 +37,9 @@ add_task(async function test_load_start() {
  * Ensure that anchor navigation invalidates shistory.
  */
 add_task(async function test_hashchange() {
-  const URL = "data:text/html;charset=utf-8,<a id=a href=%23>clickme</a>";
-
+  const PATH = getRootDirectory(gTestPath)
+              .replace("chrome://mochitests/content/", "http://example.com/");
+  const URL = PATH + "file_sessionHistory_hashchange.html";
   // Create a new tab.
   let tab = BrowserTestUtils.addTab(gBrowser, URL);
   let browser = tab.linkedBrowser;
diff --git a/browser/components/sessionstore/test/file_async_duplicate_tab.html b/browser/components/sessionstore/test/file_async_duplicate_tab.html
new file mode 100644
index 000000000000..17f1c080eacc
--- /dev/null
+++ b/browser/components/sessionstore/test/file_async_duplicate_tab.html
@@ -0,0 +1 @@
+<a href=#>clickme</a>
diff --git a/browser/components/sessionstore/test/file_async_flushes.html b/browser/components/sessionstore/test/file_async_flushes.html
new file mode 100644
index 000000000000..17f1c080eacc
--- /dev/null
+++ b/browser/components/sessionstore/test/file_async_flushes.html
@@ -0,0 +1 @@
+<a href=#>clickme</a>
diff --git a/browser/components/sessionstore/test/file_sessionHistory_hashchange.html b/browser/components/sessionstore/test/file_sessionHistory_hashchange.html
new file mode 100644
index 000000000000..4b64fc180af6
--- /dev/null
+++ b/browser/components/sessionstore/test/file_sessionHistory_hashchange.html
@@ -0,0 +1 @@
+<a id=a href=#>clickme</a>