Thought it might be an update issue as I was running FF 3.x when this issue started. I updated to 4.0 last night and it hasn't changed anything. FF opened and ran once, now not at all. No error message, no running process in task manager. Double clicking on the FF icon makes a busy icon, it shows in Task Manager, then goes away and never opens. Suggestions? =( No new software has been installed since this has occured, I've run anti-virus software, etc. Thanks for the help.