From 6f4b15e60d5d0cbd1f8be8810bc83e58cc1c4ba0 Mon Sep 17 00:00:00 2001
From: Edgar Chen <echen@mozilla.com>
Date: Tue, 4 Jun 2024 23:38:45 +0000
Subject: [PATCH] Bug 1883396 - Exit fullscreen when two Escape keyup events
 occur in a short time; r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D209667
---
 layout/base/PresShell.cpp                | 30 +++++++++++++++++++-----
 layout/base/PresShell.h                  |  4 ++++
 modules/libpref/init/StaticPrefList.yaml |  7 ++++++
 3 files changed, 35 insertions(+), 6 deletions(-)

diff --git a/layout/base/PresShell.cpp b/layout/base/PresShell.cpp
index c184b74e2d8a..6e588cff05c8 100644
--- a/layout/base/PresShell.cpp
+++ b/layout/base/PresShell.cpp
@@ -8669,12 +8669,30 @@ void PresShell::EventHandler::MaybeHandleKeyboardEventBeforeDispatch(
 
     // The event listeners in chrome can prevent this ESC behavior by
     // calling prevent default on the preceding keydown/press events.
-    if (!mPresShell->mIsLastChromeOnlyEscapeKeyConsumed &&
-        aKeyboardEvent->mMessage == eKeyUp) {
-      // ESC key released while in DOM fullscreen mode.
-      // Fully exit all browser windows and documents from
-      // fullscreen mode.
-      Document::AsyncExitFullscreen(nullptr);
+    if (aKeyboardEvent->mMessage == eKeyUp) {
+      bool shouldExitFullscreen =
+          !mPresShell->mIsLastChromeOnlyEscapeKeyConsumed;
+      if (!shouldExitFullscreen) {
+        if (mPresShell->mLastConsumedEscapeKeyUpForFullscreen &&
+            (aKeyboardEvent->mTimeStamp -
+             mPresShell->mLastConsumedEscapeKeyUpForFullscreen) <=
+                TimeDuration::FromMilliseconds(
+                    StaticPrefs::
+                        dom_fullscreen_force_exit_on_multiple_escape_interval())) {
+          shouldExitFullscreen = true;
+          mPresShell->mLastConsumedEscapeKeyUpForFullscreen = TimeStamp();
+        } else {
+          mPresShell->mLastConsumedEscapeKeyUpForFullscreen =
+              aKeyboardEvent->mTimeStamp;
+        }
+      }
+
+      if (shouldExitFullscreen) {
+        // ESC key released while in DOM fullscreen mode.
+        // Fully exit all browser windows and documents from
+        // fullscreen mode.
+        Document::AsyncExitFullscreen(nullptr);
+      }
     }
   }
 
diff --git a/layout/base/PresShell.h b/layout/base/PresShell.h
index 1f710a5897b6..97ef601287d0 100644
--- a/layout/base/PresShell.h
+++ b/layout/base/PresShell.h
@@ -3221,6 +3221,10 @@ class PresShell final : public nsStubDocumentObserver,
   bool mProcessingReflowCommands : 1;
   bool mPendingDidDoReflow : 1;
 
+  // The last TimeStamp when the keyup event did not exit fullscreen because it
+  // was consumed.
+  TimeStamp mLastConsumedEscapeKeyUpForFullscreen;
+
   struct CapturingContentInfo final {
     CapturingContentInfo()
         : mRemoteTarget(nullptr),
diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index 93186cde494d..09b1be36a8c6 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -2703,6 +2703,13 @@
   value: false
   mirror: always
 
+# The interval in milliseconds between two Escape key events where the second
+# key event will exit fullscreen, even if it is consumed.
+- name: dom.fullscreen.force_exit_on_multiple_escape_interval
+  type: uint32_t
+  value: 500
+  mirror: always
+
 # Whether the Gamepad API is enabled
 - name: dom.gamepad.enabled
   type: bool