Yesterday, I installed gnome-shell and managed to get it working after a little bit of trouble. Now I'm getting a kind of weird problem, which an image will explain better than my words can:
As you can see, Firefox's menu (just an example, it happens with every application) displays in the gnome-shell panel (same behavior as Unity has). Also, it seems to be under the panel, since you can't hover or click on it.
Any help will be appreciated.