Logging out of GMail ? Your firefox will close !

The following is my firefox version.

Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.11) Gecko/20071127 Firefox/2.0.0.11

Whenever I log out of gmail, firefox gets closed with the window you see on the left.

I use Windows Xp professional ed.