"leaves the Firefox process running"

No need to reboot on the odd occasion that FF does this, just close the process down!

FF is defintely less stable than it used to be, and surprisingly IE8 is pretty damn good.

The best would be Opera but upgrading is a real pain in the arse. Also despite best efforts such as masking as IE or FF it does not run on all sites, problems with Java / script especially. But Opera has unparalleled security and tweaking options per site, really excellent.