Comment 8 for bug 878165

@Aurélien Gâteau
I installed libdbusmenu-qt from lp:~agateau/libdbusmenu-qt/workaround-xul-bug how you suggested.
Now both firefox then thunderbird work very well, although the menu isn't perfect (sometimes there are two menu at the same time, but this behavior is very very rare).
On the contrary the patch doesn't work with seamonkey (but globalmenu for seamonkey isn't official, so it can be a seamonkey extension bug).