In Windows XP, I exit Firefox 3.6 and the browser disappears. However, when I later try to restart Firefox it will not start. In Task Manager, I checked processes tab and see "Firefox.exe" is still running. To restart Firefox, I have to stop the "Firefox.exe" process from running in Task Manager. Then, Firefox will restart normally. Some times Firefox will close properly, but several times a week, it closes the browser on my desktop but keeps running in the background. I have disabled or uninstalled all but 3 add-ons: Adblock Plus; Quick Page Zoom; and Webmail Ad Blocker. All of these add on's are up to date versions. I have cleaned the cache and run multiple malware and antivirus programs. I have run "Chkdsk" and defragmented my hard drive. I have also run Windows Registry Pro to clean out any problems there. Oddly, my wife's PC has the same operating system and the same Firefox version. She is having the same problem. She closes Firefox and it disappears. Later on, she tries to restart Firefox, but cannot. I checked her running processes and see "Firefox.exe" is still running.