turned on usage of nsViewManager2, which seems to fix some important bugs on linux, such as #20185, and definitely #21405. r=pavlov

view/src/nsViewFactory.cpp

@@ -109,7 +109,8 @@ nsresult nsViewFactory::LockFactory(PRBool aLock)
   return NS_OK;
 }
 
-#define USE_NEW_COMPOSITOR 1
+//Uncomment the following line to go back to the "new" compositor.
+//#define USE_NEW_COMPOSITOR 1
 
 #if USE_NEW_COMPOSITOR
 #include "nsViewManager.h"