What's the point ? There's absolutely no benefit in keeping Gtk+2 longer.
Gtk+ 2.24.0 has been released 3 years ago (january, 2011) and is only receiving bugfix due to existing apps who didn't move to Gtk+3.
By migrating more apps, we can drop Gtk+ 2.24 (at least from images), firefox is one of the major application that prevents us to do so.