I would have just upgraded but everything fell apart during the process. I think I saved everything off the drive. Now I'm trying to put it back together with 12. Where can I find my bookmarks in 10.04, and where do I put them in 12.04?
They should be here: .mozilla/firefox/xxxxxxxx.default/.
This xxxxx stuff is a random string of 8 characters.
If you don't see ".mozilla" folder in your old home folder you have to make nautilus to show you also hidden folders: http://www.techheadz.co.uk/253.html
When this happen , i generally look for the config directory of firefox in the old home folder and copy it to the new , it usually is .mozilla/firefox.
1)backup your current .mozilla/firefox directory
2) erase you current .mozilla/firefox
3) copy the old one to the current one
4) test it via firefox
They're are other ways to do it but i found it the most easy one
Small guide for your situation by Mozilla: http://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles