--- a/widget/gtk/nsWindow.cpp
+++ b/widget/gtk/nsWindow.cpp
@@ -5099,17 +5099,17 @@ IsFullscreenSupported(GtkWidget* aShell)
 }
 
 nsresult
 nsWindow::MakeFullScreen(bool aFullScreen, nsIScreen* aTargetScreen)
 {
     LOG(("nsWindow::MakeFullScreen [%p] aFullScreen %d\n",
          (void *)this, aFullScreen));
 
-    if (!IsFullscreenSupported(mShell)) {
+    if (mIsX11Display && !IsFullscreenSupported(mShell)) {
         return NS_ERROR_NOT_AVAILABLE;
     }
 
     if (aFullScreen) {
         if (mSizeMode != nsSizeMode_Fullscreen)
             mLastSizeMode = mSizeMode;
 
         mSizeMode = nsSizeMode_Fullscreen;