Hi Jamey,
Well, it is possible to make extensions work via a few different methods, but you should realise from the get-go that some will not work at all, especially some created for Firefox 2 will not work with Firefox 3 versions (Minefield and Gran Paradiso) for various reasons.
The method I use is to 'bump' the extension (Method 1 in the tutorial). This means you change the max version value. Instead of me trying to explain it all here, you'll find all the info you need
in this tutorial
Good luck!