Like you I was reluctant to upgrade to versions after 3 because Mozilla have seemingly lost the plot completely.
However you'll be pleased to know that you can largely make version 9 look like 3. I.e. show the menu bar, don't display tabs at the top include the bookmarks menu.
As for crashing all the time well I've not found that and if you've not upgraded then you've not found that either. I guess you've just read something negative about 9.
So embrace the newer version. After all, we don't want to sob in the corner like IE6 users right?
Alternatively just install another browser - you can run them in parallel. Use Chrome or whatever for the websites that demand a certain version of Firefox then keep version 3 for your regular surfing.