-= Because of the "delay", I've switched to Chrome.. Enjoying it.. Hoping for add-ons for Chrome..
You will be waiting a while, whilst it is undoubtedly fast, I too felt it was a poor user experience with virtually no user configuration. There are also many concerns over user privacy so much so that it has spawned SWIron chrome without the google privacy issues.
For me it has been more hype than functionality, heck we are now on version 3.0 in 9 months. For me that smacks of trying to look like a mature established program. This is more obvious when you compare it with other major browsers and how long they have been around and what version they are on.
Chrome, thanks but no thanks.
I have to say I have had no such shutdown issues with firefox 3.0 or 3.5, when I close the browser that's it is closes and its task manager entry goes immediately.
So I don't know what settings you have that might be doing anything, clearing browser history or other items or what other security software or OS settings, which might have an impact. Firefox isn't 3.5rc any longer, since I believe that you took part in the beta builds and the rc version you may well have bumped into why beta software is something which you have to fully understand there can be issues.
I would suggest complete removal of firefox (folders, registry, etc.) and ensure everything has gone and install the regular release version 3.5 and install it cleanly.