The symptom is odd enough. You let Firefox upgrade itself, and upon reopening, you lose all your saved tabs and bookmarks. Is it Firefox screwing up and losing all your saved tabs after an upgrade? Or is it because you're on Mac OS X 10.6.8 with an encrypted home folder?
For reasons I know not, Mac OS X can split your home Library folder into two pieces (on Mac OS X 10.6.8 with an encrypted home folder). Supposing your username is hsimpson, then one of your Library folders (the usual one) is inside the encrypted home folder, in the usual ~/Library. The other one is in /Users/.hsimpson.
Best way to tell if Firefox is using the wrong Library folder is to open the Firefox profile manager. Go to the Terminal, and type in something like:
Of course, firefox-bin is the actual executable on a Mac, hidden inside the Firefox.app application bundle (really just a special folder). With the profile manager open, hovering the mouse over a profile name will display the directory path to where the profile is stored.
You may have to do some experimentation to figure out which is the "true" profile folder with the most up to date tabs and bookmarks (I suggest you backup all potential profile folders), but with some experimentation, you should be able to point Firefox back to using the correct profile folder.
I would know: I've had to do this more than a few times.