--- a/dom/base/ScreenOrientation.cpp
+++ b/dom/base/ScreenOrientation.cpp
@@ -473,17 +473,17 @@ ScreenOrientation::GetLockOrientationPer
   }
 
   if (Preferences::GetBool("dom.screenorientation.testing.non_fullscreen_lock_allow",
                            false)) {
     return LOCK_ALLOWED;
   }
 
   // Other content must be full-screen in order to lock orientation.
-  return doc->MozFullScreen() ? FULLSCREEN_LOCK_ALLOWED : LOCK_DENIED;
+  return doc->Fullscreen() ? FULLSCREEN_LOCK_ALLOWED : LOCK_DENIED;
 }
 
 nsIDocument*
 ScreenOrientation::GetResponsibleDocument() const
 {
   nsCOMPtr<nsPIDOMWindowInner> owner = GetOwner();
   if (!owner) {
     return nullptr;
@@ -642,17 +642,17 @@ ScreenOrientation::FullScreenEventListen
   MOZ_ASSERT(target);
 
   nsCOMPtr<nsIDocument> doc = do_QueryInterface(target);
   MOZ_ASSERT(doc);
 
   // We have to make sure that the event we got is the event sent when
   // fullscreen is disabled because we could get one when fullscreen
   // got enabled if the lock call is done at the same moment.
-  if (doc->MozFullScreen()) {
+  if (doc->Fullscreen()) {
     return NS_OK;
   }
 
   hal::UnlockScreenOrientation();
 
   nsresult rv = target->RemoveSystemEventListener(NS_LITERAL_STRING("fullscreenchange"),
                                                   this, true);
   NS_ENSURE_SUCCESS(rv, rv);

--- a/dom/base/nsDocument.cpp
+++ b/dom/base/nsDocument.cpp
@@ -12170,17 +12170,17 @@ nsDocument::GetFullscreenElement()
                element->IsFullScreenAncestor(),
     "Fullscreen element should have fullscreen styles applied");
   return element;
 }
 
 NS_IMETHODIMP
 nsDocument::GetMozFullScreen(bool *aFullScreen)
 {
-  *aFullScreen = MozFullScreen();
+  *aFullScreen = Fullscreen();
   return NS_OK;
 }
 
 NS_IMETHODIMP
 nsDocument::GetMozFullScreenEnabled(bool *aFullScreen)
 {
   NS_ENSURE_ARG_POINTER(aFullScreen);
   *aFullScreen = FullscreenEnabled();

--- a/dom/base/nsIDocument.h
+++ b/dom/base/nsIDocument.h
@@ -2555,17 +2555,17 @@ public:
   Element* GetCurrentScript();
   void ReleaseCapture() const;
   virtual void MozSetImageElement(const nsAString& aImageElementId,
                                   Element* aElement) = 0;
   nsIURI* GetDocumentURIObject() const;
   // Not const because all the full-screen goop is not const
   virtual bool FullscreenEnabled() = 0;
   virtual Element* GetFullscreenElement() = 0;
-  bool MozFullScreen()
+  bool Fullscreen()
   {
     return !!GetFullscreenElement();
   }
   void ExitFullscreen();
   Element* GetMozPointerLockElement();
   void MozExitPointerLock()
   {
     UnlockPointer(this);

--- a/dom/html/test/file_fullscreen-api.html
+++ b/dom/html/test/file_fullscreen-api.html
@@ -51,32 +51,34 @@ function sendMouseClick(element) {
 }
 
 function fullScreenElement() {
   return document.getElementById('full-screen-element');
 }
 
 function enter1(event) {
   is(event.target, document, "Event target should be full-screen document #1");
+  ok(document.fullscreen, "Document should be in fullscreen");
   is(document.fullscreenElement, fullScreenElement(),
      "Full-screen element should be div element.");
   ok(document.fullscreenElement.matches(":fullscreen"),
      "FSE should match :fullscreen");
   var fse = fullScreenElement();
   addFullscreenChangeContinuation("exit", exit1);
   fse.parentNode.removeChild(fse);
   is(document.fullscreenElement, null,
      "Full-screen element should be null after removing.");
   document.body.appendChild(fse);
   is(document.fullscreenElement, null,
      "Full-screen element should still be null after re-adding former FSE.");
 }
 
 function exit1(event) {
   is(event.target, document, "Event target should be full-screen document #2");
+  ok(!document.fullscreen, "Document should not be in fullscreen");
   is(document.fullscreenElement, null, "Full-screen element should be null.");
   iframe = document.createElement("iframe");
   iframe.allowFullscreen = true;
   addFullscreenChangeContinuation("enter", enter2);
   document.body.appendChild(iframe);
   iframe.src = iframeContents;
 }
 

--- a/dom/html/test/file_fullscreen-lenient-setters.html
+++ b/dom/html/test/file_fullscreen-lenient-setters.html
@@ -20,16 +20,25 @@ function is(a, b, msg) {
 
 function info(msg) {
   opener.info("[lenient-setters] " + msg);
 }
 
 let unattachedDiv = document.createElement("div");
 
 function begin() {
+  var originalValue = document.fullscreen;
+  try {
+    document.fullscreen = !document.fullscreen;
+    is(document.fullscreen, originalValue,
+       "fullscreen should not be changed");
+  } catch (e) {
+    ok(false, "Setting fullscreen should not throw");
+  }
+
   var originalElem = document.fullscreenElement;
   try {
     document.fullscreenElement = unattachedDiv;
     document.fullscreenElement = [];
     is(document.fullscreenElement, originalElem,
        "fullscreenElement should not be changed");
   } catch (e) {
     ok(false, "Setting fullscreenElement should not throw");

--- a/dom/html/test/file_fullscreen-unprefix-disabled-inner.html
+++ b/dom/html/test/file_fullscreen-unprefix-disabled-inner.html
@@ -26,16 +26,17 @@ SimpleTest.requestFlakyTimeout(
   "need to wait for a while to confirm no unexpected event is dispatched");
 
 let div = document.getElementById("fullscreen");
 let unattachedDiv = document.createElement('div');
 
 function begin() {
   ok(!("requestFullscreen" in div), "No element.requestFullscreen");
   ok(!("exitFullscreen" in document), "No document.exitFullscreen");
+  ok(!("fullscreen" in document), "No document.fullscreen");
   ok(!("fullscreenElement" in document), "No document.fullscreenElement");
   ok(!("fullscreenEnabled" in document), "No document.fullscreenEnabled");
   ok(!("onfullscreenchange" in document), "No document.onfullscreenchange");
   ok(!("onfullscreenerror" in document), "No document.onfullscreenerror");
 
   for (var event of ["fullscreenchange", "fullscreenerror"]) {
     let customEvent = new Event(event, {bubbles: true});
     let gotCustomEventFromWindow = false;

--- a/dom/webidl/Document.webidl
+++ b/dom/webidl/Document.webidl
@@ -220,32 +220,32 @@ partial interface Document {
 
 };
 
 // https://fullscreen.spec.whatwg.org/#api
 partial interface Document {
   // Note: Per spec the 'S' in these two is lowercase, but the "Moz"
   // versions hve it uppercase.
   [LenientSetter, Func="nsDocument::IsUnprefixedFullscreenEnabled"]
+  readonly attribute boolean fullscreen;
+  [BinaryName="fullscreen", Deprecated="PrefixedFullscreenAPI"]
+  readonly attribute boolean mozFullScreen;
+  [LenientSetter, Func="nsDocument::IsUnprefixedFullscreenEnabled"]
   readonly attribute boolean fullscreenEnabled;
   [BinaryName="fullscreenEnabled", Deprecated="PrefixedFullscreenAPI"]
   readonly attribute boolean mozFullScreenEnabled;
   [LenientSetter, Func="nsDocument::IsUnprefixedFullscreenEnabled"]
   readonly attribute Element? fullscreenElement;
   [BinaryName="fullscreenElement", Deprecated="PrefixedFullscreenAPI"]
   readonly attribute Element? mozFullScreenElement;
 
   [Func="nsDocument::IsUnprefixedFullscreenEnabled"]
   void exitFullscreen();
   [BinaryName="exitFullscreen", Deprecated="PrefixedFullscreenAPI"]
   void mozCancelFullScreen();
-
-  // Gecko-specific fullscreen bits
-  [Deprecated="PrefixedFullscreenAPI"]
-  readonly attribute boolean mozFullScreen;
 };
 
 // http://dvcs.w3.org/hg/pointerlock/raw-file/default/index.html#extensions-to-the-document-interface
 partial interface Document {
     readonly attribute Element? mozPointerLockElement;
     void mozExitPointerLock ();
 };