Disable plugins on birch. They are causing ANR on the droid pro

--HG--
extra : rebase_source : 0ad7e38c50e61be05fad85c7b6bf40a88bee7666

mobile/app/mobile.js

@@ -439,7 +439,7 @@ pref("browser.ui.touch.weight.visited", 120); // percentage
 pref("plugin.disable", false);
 pref("dom.ipc.plugins.enabled", true);
 #elifdef ANDROID
-pref("plugin.disable", false);
+pref("plugin.disable", true);
 pref("dom.ipc.plugins.enabled", false);
 #else
 pref("plugin.disable", true);