This geek tip is coming to you from the school of hard knocks — after downloading the new version of Firefox 3 (currently in Beta) on one of my computers, I was dismayed to find all my add-ons were gone. I know, you're shaking your head and saying "duh!," but I thought I'd let my mistake be a warning to you. A warning will pop up that some add-ons are incompatible and it can check if there are newer compatible versions.
However, this geek got a tip from another geek: If you want to use the new, speedier Firefox 3, you can always download this in addition to your current version, that is, download it to your desktop instead of replacing your current Firefox. And a forewarning: The aesthetics of the new Firefox aren't exactly gorgeous, if you care about that sort of thing.