Bug 1725371 - Reenable Gnome subsurface workaround,

This workaround was removed in D121650. Unfortunately we need it
a bit longer until the Mutter fix reaches users, as triggering it
crashes the whole desktop.

Differential Revision: https://phabricator.services.mozilla.com/D122460

widget/gtk/nsWindow.cpp

@@ -5919,8 +5919,11 @@ void nsWindow::ResumeCompositorHiddenWindow() {
 // pause the compositor and destroy EGLSurface & resume the compositor
 // and re-create EGLSurface on next expose event.
 void nsWindow::PauseCompositorHiddenWindow() {
-  if (!mIsAccelerated || mIsDestroyed ||
-      mCompositorState == COMPOSITOR_PAUSED_INITIALLY) {
+  // TODO: The compositor backend currently relies on the pause event to work
+  // around a Gnome specific bug. Remove again once the fix is widely available.
+  // See bug 1721298
+  if ((!mIsAccelerated && !gfx::gfxVars::UseWebRenderCompositor()) ||
+      mIsDestroyed || mCompositorState == COMPOSITOR_PAUSED_INITIALLY) {
     return;
   }