Firefox 3.6.3 crashed and would not reload as the system informed that firefox was already running. Rebooting had no effect. 3.6.4 was downloaded and installed. It would not run for the same reason. Windows XP was then upgraded to SP2. No change. 3.6.4 was uninstalled with no problem but 3.6.3 refuses to install. (When 'remove' is clicked, there is disc activity for about a second but then all stops.) No files have been deleted by me. There is no indication that I can see inspecting 'processes' or msconfig to indicate that Firefox is running.