I hit some problems with Firefox’s two-pane appmenu, because popups from the first pane can obscure items in the second.
Currently I am working with this single pane menu, which is similar to the menu in Opera 18. Apart from being a long menu I think this is a good layout.
I want to have recent downloads show in a popup and use a splitmenu for that entry. I think this is more important now that all the surrounding entries are splitmenus.