--- a/dom/base/nsDOMWindowUtils.cpp
+++ b/dom/base/nsDOMWindowUtils.cpp
@@ -3149,16 +3149,17 @@ private:
   nsSize mSize;
 };
 
 LinkedList<OldWindowSize> OldWindowSize::sList;
 
 NS_IMETHODIMP
 nsDOMWindowUtils::HandleFullscreenRequests(bool* aRetVal)
 {
+  PROFILER_MARKER("Enter fullscreen");
   nsCOMPtr<nsIDocument> doc = GetDocument();
   NS_ENSURE_STATE(doc);
 
   // Notify the pres shell that we are starting fullscreen change, and
   // set the window dimensions in advance. Since the resize message
   // comes after the fullscreen change call, doing so could avoid an
   // extra resize reflow after this point.
   nsRect screenRect;
@@ -3171,16 +3172,17 @@ nsDOMWindowUtils::HandleFullscreenReques
 
   *aRetVal = nsIDocument::HandlePendingFullscreenRequests(doc);
   return NS_OK;
 }
 
 nsresult
 nsDOMWindowUtils::ExitFullscreen()
 {
+  PROFILER_MARKER("Exit fullscreen");
   nsCOMPtr<nsIDocument> doc = GetDocument();
   NS_ENSURE_STATE(doc);
 
   // Although we would not use the old size if we have already exited
   // fullscreen, we still want to cleanup in case we haven't.
   nsSize oldSize = OldWindowSize::GetAndRemove(doc->GetWindow());
   if (!doc->GetFullscreenElement()) {
     return NS_OK;

--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -5944,17 +5944,19 @@ private:
     // transition on the widget.
     eBeforeToggle,
     // ToggleFullscreen stage actually executes the fullscreen toggle,
     // and wait for the next paint on the content to continue.
     eToggleFullscreen,
     // AfterToggle stage happens after we toggle the fullscreen state.
     // In this stage, the task triggers the post-toggle fullscreen
     // transition on the widget.
-    eAfterToggle
+    eAfterToggle,
+    // End stage is triggered after the final transition finishes.
+    eEnd
   };
 
   class Observer final : public nsIObserver
   {
   public:
     NS_DECL_ISUPPORTS
     NS_DECL_NSIOBSERVER
 
@@ -5990,20 +5992,22 @@ FullscreenTransitionTask::Run()
   mStage = Stage(mStage + 1);
   if (MOZ_UNLIKELY(mWidget->Destroyed())) {
     // If the widget has been destroyed before we get here, don't try to
     // do anything more. Just let it go and release ourselves.
     NS_WARNING("The widget to fullscreen has been destroyed");
     return NS_OK;
   }
   if (stage == eBeforeToggle) {
+    PROFILER_MARKER("Fullscreen transition start");
     mWidget->PerformFullscreenTransition(nsIWidget::eBeforeFullscreenToggle,
                                          mDuration.mFadeIn, mTransitionData,
                                          this);
   } else if (stage == eToggleFullscreen) {
+    PROFILER_MARKER("Fullscreen toggle start");
     if (MOZ_UNLIKELY(mWindow->mFullScreen != mFullscreen)) {
       // This could happen in theory if several fullscreen requests in
       // different direction happen continuously in a short time. We
       // need to ensure the fullscreen state matches our target here,
       // otherwise the widget would change the window state as if we
       // toggle for Fullscreen Mode instead of Fullscreen API.
       NS_WARNING("The fullscreen state of the window does not match");
       mWindow->mFullScreen = mFullscreen;
@@ -6033,16 +6037,18 @@ FullscreenTransitionTask::Run()
     mTimer = do_CreateInstance(NS_TIMER_CONTRACTID);
     uint32_t timeout =
       Preferences::GetUint("full-screen-api.transition.timeout", 500);
     mTimer->Init(observer, timeout, nsITimer::TYPE_ONE_SHOT);
   } else if (stage == eAfterToggle) {
     mWidget->PerformFullscreenTransition(nsIWidget::eAfterFullscreenToggle,
                                          mDuration.mFadeOut, mTransitionData,
                                          this);
+  } else if (stage == eEnd) {
+    PROFILER_MARKER("Fullscreen transition end");
   }
   return NS_OK;
 }
 
 NS_IMPL_ISUPPORTS(FullscreenTransitionTask::Observer, nsIObserver)
 
 NS_IMETHODIMP
 FullscreenTransitionTask::Observer::Observe(nsISupports* aSubject,
@@ -6053,26 +6059,28 @@ FullscreenTransitionTask::Observer::Obse
   if (strcmp(aTopic, FullscreenTransitionTask::kPaintedTopic) == 0) {
     nsCOMPtr<nsPIDOMWindowInner> win(do_QueryInterface(aSubject));
     nsCOMPtr<nsIWidget> widget = win ?
       nsGlobalWindow::Cast(win)->GetMainWidget() : nullptr;
     if (widget == mTask->mWidget) {
       // The paint notification arrives first. Cancel the timer.
       mTask->mTimer->Cancel();
       shouldContinue = true;
+      PROFILER_MARKER("Fullscreen toggle end");
     }
   } else {
 #ifdef DEBUG
     MOZ_ASSERT(strcmp(aTopic, NS_TIMER_CALLBACK_TOPIC) == 0,
                "Should only get fullscreen-painted or timer-callback");
     nsCOMPtr<nsITimer> timer(do_QueryInterface(aSubject));
     MOZ_ASSERT(timer && timer == mTask->mTimer,
                "Should only trigger this with the timer the task created");
 #endif
     shouldContinue = true;
+    PROFILER_MARKER("Fullscreen toggle timeout");
   }
   if (shouldContinue) {
     nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
     obs->RemoveObserver(this, kPaintedTopic);
     mTask->mTimer = nullptr;
     mTask->Run();
   }
   return NS_OK;