Comment 2 for bug 488857

I see this bug as well, in Firefox (both 3.0.x and mozilla-central) and in Thunderbird (3.0b3pre).

From my experience, this bug became an issue when I upgraded to Ubuntu Jaunty. I think it might be a bug in newer versions of the GTK library.

Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.10) Gecko/2009042523 Ubuntu/9.04 (jaunty) Firefox/3.0.10
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2a1pre) Gecko/20090519 Minefield/3.6a1pre
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1b5pre) Gecko/20090515 Shredder/3.0b3pre

My buggy machine has GTK version 2.16.1-0ubuntu2.
A different NON-buggy machine (running Hardy I think) has GTK version 2.12.9-3ubuntu5

(gtk versions obtained via "apt-cache show libgtk2.0-common | grep Version")