--- a/dom/base/nsGkAtomList.h
+++ b/dom/base/nsGkAtomList.h
@@ -2061,19 +2061,16 @@ GK_ATOM(onmozorientationchange, "onmozor
 GK_ATOM(onuserproximity, "onuserproximity")
 
 // light sensor support
 GK_ATOM(ondevicelight, "ondevicelight")
 
 // MediaDevices device change event
 GK_ATOM(ondevicechange, "ondevicechange")
 
-// HTML element attributes that only exposed to XBL and chrome content
-GK_ATOM(mozinputrangeignorepreventdefault, "mozinputrangeignorepreventdefault")
-
 // WebExtensions
 GK_ATOM(moz_extension, "moz-extension")
 GK_ATOM(all_urlsPermission, "<all_urls>")
 GK_ATOM(clipboardRead, "clipboardRead")
 GK_ATOM(clipboardWrite, "clipboardWrite")
 GK_ATOM(debugger, "debugger")
 GK_ATOM(tabs, "tabs")
 GK_ATOM(webRequestBlocking, "webRequestBlocking")

--- a/dom/html/HTMLInputElement.cpp
+++ b/dom/html/HTMLInputElement.cpp
@@ -4695,18 +4695,17 @@ HTMLInputElement::PostHandleEvent(EventC
   return MaybeInitPickers(aVisitor);
 }
 
 void
 HTMLInputElement::PostHandleEventForRangeThumb(EventChainPostVisitor& aVisitor)
 {
   MOZ_ASSERT(mType == NS_FORM_INPUT_RANGE);
 
-  if ((nsEventStatus_eConsumeNoDefault == aVisitor.mEventStatus &&
-       !MozInputRangeIgnorePreventDefault()) ||
+  if (nsEventStatus_eConsumeNoDefault == aVisitor.mEventStatus ||
       !(aVisitor.mEvent->mClass == eMouseEventClass ||
         aVisitor.mEvent->mClass == eTouchEventClass ||
         aVisitor.mEvent->mClass == eKeyboardEventClass)) {
     return;
   }
 
   nsRangeFrame* rangeFrame = do_QueryFrame(GetPrimaryFrame());
   if (!rangeFrame && mIsDraggingRange) {

--- a/dom/html/HTMLInputElement.h
+++ b/dom/html/HTMLInputElement.h
@@ -857,22 +857,16 @@ public:
   int32_t InputTextLength(CallerType aCallerType);
 
   void MozGetFileNameArray(nsTArray<nsString>& aFileNames, ErrorResult& aRv);
 
   void MozSetFileNameArray(const Sequence< nsString >& aFileNames, ErrorResult& aRv);
   void MozSetFileArray(const Sequence<OwningNonNull<File>>& aFiles);
   void MozSetDirectory(const nsAString& aDirectoryPath, ErrorResult& aRv);
 
-  bool MozInputRangeIgnorePreventDefault() const
-  {
-    return (IsInChromeDocument() || IsInNativeAnonymousSubtree()) &&
-      GetBoolAttr(nsGkAtoms::mozinputrangeignorepreventdefault);
-  }
-
   /*
    * The following functions are called from datetime picker to let input box
    * know the current state of the picker or to update the input box on changes.
    */
   void GetDateTimeInputBoxValue(DateTimeValue& aValue);
   void UpdateDateTimeInputBox(const DateTimeValue& aValue);
   void SetDateTimePickerState(bool aOpen);
 
@@ -1536,17 +1530,17 @@ protected:
   bool IsPopupBlocked() const;
 
   GetFilesHelper* GetOrCreateGetFilesHelper(bool aRecursiveFlag,
                                             ErrorResult& aRv);
 
   void ClearGetFilesHelpers();
 
   /**
-   * nsINode::SetMayBeApzAware() will be invoked in this function if necessary
+   * nsINode::SetMayBeApzAware() will be invoked in this function if necessary 
    * to prevent default action of APZC so that we can increase/decrease the
    * value of this InputElement when mouse wheel event comes without scrolling
    * the page.
    *
    * SetMayBeApzAware() will set flag MayBeApzAware which is checked by apzc to
    * decide whether to add this element into its dispatch-to-content region.
    */
   void UpdateApzAwareFlag();

--- a/dom/html/test/forms/chrome.ini
+++ b/dom/html/test/forms/chrome.ini
@@ -1,6 +1,5 @@
 [DEFAULT]
 support-files =
   submit_invalid_file.sjs
 [test_autocompleteinfo.html]
 [test_submit_invalid_file.html]
-[test_input_range_mozinputrangeignorepreventdefault_chrome.html]

--- a/dom/html/test/forms/mochitest.ini
+++ b/dom/html/test/forms/mochitest.ini
@@ -56,17 +56,16 @@ skip-if = os == "android"
 skip-if = os == "android"
 [test_input_number_validation.html]
 # We don't build ICU for Firefox for Android:
 skip-if = os == "android"
 [test_input_number_focus.html]
 [test_input_range_attr_order.html]
 [test_input_range_key_events.html]
 [test_input_range_mouse_and_touch_events.html]
-[test_input_range_mozinputrangeignorepreventdefault.html]
 [test_input_range_rounding.html]
 [test_input_sanitization.html]
 skip-if = os == 'android' && debug # Extremely slow on debug android
 [test_input_textarea_set_value_no_scroll.html]
 [test_input_time_key_events.html]
 [test_input_time_sec_millisec_field.html]
 [test_input_types_pref.html]
 [test_input_typing_sanitization.html]

deleted file mode 100644
--- a/dom/html/test/forms/test_input_range_mozinputrangeignorepreventdefault.html
+++ /dev/null
@@ -1,94 +0,0 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-https://bugzilla.mozilla.org/show_bug.cgi?id=1338961
--->
-<head>
-  <title>Test mouse and touch events for range</title>
-  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
-  <script type="text/javascript" src="/tests/SimpleTest/EventUtils.js"></script>
-  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
-  <meta charset="UTF-8">
-  <meta name="viewport" content="width=device-width, initial-scale=1.0">
-  <style>
-    /* synthesizeMouse and synthesizeFunc uses getBoundingClientRect. We set
-     * the following properties to avoid fractional values in the rect returned
-     * by getBoundingClientRect in order to avoid rounding that would occur
-     * when event coordinates are internally converted to be relative to the
-     * top-left of the element. (Such rounding would make it difficult to
-     * predict exactly what value the input should take on for events at
-     * certain coordinates.)
-     */
-    input { margin: 0 ! important; width: 200px ! important; }
-  </style>
-</head>
-<body>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1338961">Mozilla Bug 1338961</a>
-<p id="display"></p>
-<div id="content">
-  <input id="range" type="range" mozinputrangeignorepreventdefault="true">
-</div>
-<pre id="test">
-<script type="application/javascript">
-
-/**
- * Test for Bug 1338961
- * This test ensures mozinputrangeignorepreventdefault has no effect in
- * content html.
- **/
-SimpleTest.waitForExplicitFinish();
-SimpleTest.waitForFocus(function() {
-  test(synthesizeMouse, "click", "mousedown", "mousemove", "mouseup");
-  test(synthesizeTouch, "tap", "touchstart", "touchmove", "touchend");
-  SimpleTest.finish();
-});
-
-function flush() {
-  // Flush style, specifically to flush the 'direction' property so that the
-  // browser uses the new value for thumb positioning.
-  var flush = document.body.clientWidth;
-}
-
-const QUARTER_OF_RANGE = "25";
-
-function test(synthesizeFunc, clickOrTap, startName, moveName, endName) {
-  var elem = document.getElementById("range");
-  elem.focus();
-  flush();
-
-  var width = parseFloat(window.getComputedStyle(elem).width);
-  var height = parseFloat(window.getComputedStyle(elem).height);
-  var borderLeft = parseFloat(window.getComputedStyle(elem).borderLeftWidth);
-  var borderTop = parseFloat(window.getComputedStyle(elem).borderTopWidth);
-  var paddingLeft = parseFloat(window.getComputedStyle(elem).paddingLeft);
-  var paddingTop = parseFloat(window.getComputedStyle(elem).paddingTop);
-
-  // Extrema for mouse/touch events:
-  var midY = height / 2 + borderTop + paddingTop;
-  var minX = borderLeft + paddingLeft;
-  var midX = minX + width / 2;
-  var maxX = minX + width;
-
-  function preventDefault(e) {
-    e.preventDefault();
-  }
-
-  // Test that preventDefault() works:
-  elem.value = QUARTER_OF_RANGE;
-  elem.addEventListener(startName, preventDefault);
-  synthesizeFunc(elem, midX, midY, {});
-  is(elem.value, QUARTER_OF_RANGE, "Test that preventDefault() works");
-  elem.removeEventListener(startName, preventDefault);
-
-  // Test that preventDefault() on the parent node works:
-  elem.value = QUARTER_OF_RANGE;
-  elem.parentNode.addEventListener(startName, preventDefault);
-  synthesizeFunc(elem, midX, midY, {});
-  is(elem.value, QUARTER_OF_RANGE, "Test that preventDefault() on the parent node works");
-  elem.parentNode.removeEventListener(startName, preventDefault);
-}
-
-</script>
-</pre>
-</body>
-</html>

deleted file mode 100644
--- a/dom/html/test/forms/test_input_range_mozinputrangeignorepreventdefault_chrome.html
+++ /dev/null
@@ -1,95 +0,0 @@
-<!DOCTYPE HTML>
-<html>
-<!--
-https://bugzilla.mozilla.org/show_bug.cgi?id=1338961
--->
-<head>
-  <title>Test mouse and touch events for range</title>
-  <script type="application/javascript" src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
-  <script type="text/javascript" src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"></script>
-  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
-  <meta charset="UTF-8">
-  <meta name="viewport" content="width=device-width, initial-scale=1.0">
-  <style>
-    /* synthesizeMouse and synthesizeFunc uses getBoundingClientRect. We set
-     * the following properties to avoid fractional values in the rect returned
-     * by getBoundingClientRect in order to avoid rounding that would occur
-     * when event coordinates are internally converted to be relative to the
-     * top-left of the element. (Such rounding would make it difficult to
-     * predict exactly what value the input should take on for events at
-     * certain coordinates.)
-     */
-    input { margin: 0 ! important; width: 200px ! important; }
-  </style>
-</head>
-<body>
-<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1338961">Mozilla Bug 1338961</a>
-<p id="display"></p>
-<div id="content">
-  <input id="range" type="range" mozinputrangeignorepreventdefault="true">
-</div>
-<pre id="test">
-<script type="application/javascript">
-
-/**
- * Test for Bug 1338961
- * This test ensures mozinputrangeignorepreventdefault has it's desired effect in
- * chrome html.
- **/
-SimpleTest.waitForExplicitFinish();
-SimpleTest.waitForFocus(function() {
-  test(synthesizeMouse, "click", "mousedown", "mousemove", "mouseup");
-  test(synthesizeTouch, "tap", "touchstart", "touchmove", "touchend");
-  SimpleTest.finish();
-});
-
-function flush() {
-  // Flush style, specifically to flush the 'direction' property so that the
-  // browser uses the new value for thumb positioning.
-  var flush = document.body.clientWidth;
-}
-
-const MIDDLE_OF_RANGE = "50";
-const QUARTER_OF_RANGE = "25";
-
-function test(synthesizeFunc, clickOrTap, startName, moveName, endName) {
-  var elem = document.getElementById("range");
-  elem.focus();
-  flush();
-
-  var width = parseFloat(window.getComputedStyle(elem).width);
-  var height = parseFloat(window.getComputedStyle(elem).height);
-  var borderLeft = parseFloat(window.getComputedStyle(elem).borderLeftWidth);
-  var borderTop = parseFloat(window.getComputedStyle(elem).borderTopWidth);
-  var paddingLeft = parseFloat(window.getComputedStyle(elem).paddingLeft);
-  var paddingTop = parseFloat(window.getComputedStyle(elem).paddingTop);
-
-  // Extrema for mouse/touch events:
-  var midY = height / 2 + borderTop + paddingTop;
-  var minX = borderLeft + paddingLeft;
-  var midX = minX + width / 2;
-  var maxX = minX + width;
-
-  function preventDefault(e) {
-    e.preventDefault();
-  }
-
-  // Test that preventDefault() is ignored:
-  elem.value = QUARTER_OF_RANGE;
-  elem.addEventListener(startName, preventDefault);
-  synthesizeFunc(elem, midX, midY, {});
-  is(elem.value, MIDDLE_OF_RANGE, "Test that preventDefault() is ignored");
-  elem.removeEventListener(startName, preventDefault);
-
-  // Test that preventDefault() on the parent node works:
-  elem.value = QUARTER_OF_RANGE;
-  elem.parentNode.addEventListener(startName, preventDefault);
-  synthesizeFunc(elem, midX, midY, {});
-  is(elem.value, MIDDLE_OF_RANGE, "Test that preventDefault() on the parent node is ignored");
-  elem.parentNode.removeEventListener(startName, preventDefault);
-}
-
-</script>
-</pre>
-</body>
-</html>

--- a/toolkit/content/widgets/videocontrols.xml
+++ b/toolkit/content/widgets/videocontrols.xml
@@ -155,31 +155,31 @@
                   tabindex="-1"/>
           <div anonid="scrubberStack" class="scrubberStack progressContainer" role="none">
             <div class="progressBackgroundBar stackItem" role="none">
               <div class="progressStack" role="none">
                 <progress anonid="bufferBar" class="bufferBar" value="0" max="100" tabindex="-1"></progress>
                 <progress anonid="progressBar" class="progressBar" value="0" max="100" tabindex="-1"></progress>
               </div>
             </div>
-            <input type="range" anonid="scrubber" class="scrubber" tabindex="-1" mozinputrangeignorepreventdefault="true" />
+            <input type="range" anonid="scrubber" class="scrubber" tabindex="-1"/>
           </div>
           <span anonid="positionLabel" class="positionLabel" role="presentation"></span>
           <span anonid="durationLabel" class="durationLabel" role="presentation"></span>
           <span anonid="positionDurationBox" class="positionDurationBox" aria-hidden="true">
             &positionAndDuration.nameFormat;
           </span>
           <div anonid="controlBarSpacer" class="controlBarSpacer" hidden="true" role="none"></div>
           <button anonid="muteButton"
                   class="muteButton"
                   mutelabel="&muteButton.muteLabel;"
                   unmutelabel="&muteButton.unmuteLabel;"
                   tabindex="-1"/>
           <div anonid="volumeStack" class="volumeStack progressContainer" role="none">
-            <input type="range" anonid="volumeControl" class="volumeControl" min="0" max="100" step="1" tabindex="-1" mozinputrangeignorepreventdefault="true" />
+            <input type="range" anonid="volumeControl" class="volumeControl" min="0" max="100" step="1" tabindex="-1"/>
           </div>
           <button anonid="closedCaptionButton" class="closedCaptionButton"/>
           <button anonid="fullscreenButton"
                   class="fullscreenButton"
                   enterfullscreenlabel="&fullscreenButton.enterfullscreenlabel;"
                   exitfullscreenlabel="&fullscreenButton.exitfullscreenlabel;"/>
         </div>
         <div anonid="textTrackList" class="textTrackList" hidden="true" offlabel="&closedCaption.off;"></div>