After loading: window.open ('about:mozilla', 'test2', 'chrome=no,width=320,height=240'); in the Error Console and subsequently closing the window, I see no problem. Does it also fail in safe-mode / with a new profile? http://support.mozilla.com/en-US/kb/Troubleshooting+extensions+and+themes http://support.mozilla.com/en-US/kb/Basic+Troubleshooting#Make_a_new_profile
It seems to be working now... you're magic!
I know ;)