Here's the thing. Running SimplyMepis 6 When I try to start Firefox, I can see it open for a quick second then close as soon as session manager starts. I tried creating a new profile and when I go to the new profile Firefox starts with no problem at all. So I'm guessing there's must me a problem with my default profile or the session manager itself. How do I fix this?

Try just deleting your default profile outright. Then re-create it, but before doing that, save your bookmarks and cookies as needed (save them to another directory, then simply re-copy them back to your new default profile)

Another possibility ... if your home page happens to have non-standard javascript, Firefox will often crash.

Thanks but I don't wanna do that. My bookmark is always backed-up thanks to the backup-bookmark extension but I have so many extensions there that I don't wanna go through re-installing them.
I was hoping there's a way to be able to force Firefox to start in the default profile without the svaed session, because I'm pretty sure it's one of the sites that's causing it to crash.

Only if there's no other way around it, I would go ahead and delete the profile altogether.

That's what I think too, not the home page though (it's Google), but since I have 'start with saved session' checked, I think one of the sites that are in my last saved session is messing Firefox up at startup.