Comment 14 for bug 220798

I am running Xubuntu 8.04 with Firefox 3.01 installed and I am experiencing the same problem. Installing Firefox-gnome-support also fixed the problem here.

Nevertheless, this should somehow be fixed in the original download (through the 'add/remove software' function) as new X/K/Ubuntu users (like myself) will have some trouble/inexperience in finding the solution and fixing it like suggested here.