WFM: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.6a) Gecko/20031011
I've been able to reproduce the problem in second computer with similar specs. The problem started when I installed this extension: tabextensions_en.xpi v1.9.2003101801 (latest version) It can be downloaded from here: http://white.sakura.ne.jp/~piro/xul/_tabextensions.html.en#download
Previous version on the extensin (1.8.2003082001) works fine where latest failed. Since the bug is most likely on the extension side, I suppose it can be marked as "invalid" and closed.
WFM, 2003-10-16-05 trunk ans Mozilla 1.5 Linux. (I have sent a mail to firstname.lastname@example.org about the issue). -> INVALID
(I got a reply from Piro and there is now a testing version with a fix for this problem available.)