Bug 1702855 - Disable three-finger touchpad pinch gestures on Linux by default. r=tnikkel

Differential Revision: https://phabricator.services.mozilla.com/D111201

modules/libpref/init/StaticPrefList.yaml

@@ -526,6 +526,11 @@
     type: RelaxedAtomicBool
     value: true
     mirror: always
+
+-   name: apz.gtk.touchpad_pinch.three_fingers.enabled
+    type: RelaxedAtomicBool
+    value: false
+    mirror: always
 #endif
 
 - name: apz.keyboard.enabled

widget/gtk/nsWindow.cpp

@@ -4287,6 +4287,14 @@ bool nsWindow::IsHandlingTouchSequence(GdkEventSequence* aSequence) {
 
 gboolean nsWindow::OnTouchpadPinchEvent(GdkEventTouchpadPinch* aEvent) {
   if (StaticPrefs::apz_gtk_touchpad_pinch_enabled()) {
+    // Do not respond to pinch gestures involving more than two fingers
+    // unless specifically preffed on. These are sometimes hooked up to other
+    // actions at the desktop environment level and having the browser also
+    // pinch can be undesirable.
+    if (aEvent->n_fingers > 2 &&
+        !StaticPrefs::apz_gtk_touchpad_pinch_three_fingers_enabled()) {
+      return FALSE;
+    }
     PinchGestureInput::PinchGestureType pinchGestureType =
         PinchGestureInput::PINCHGESTURE_SCALE;
     ScreenCoord CurrentSpan;