I'm having the same problem: when I run firefox it loads up, and sometimes starts opening the previous pages, then crashes. Running firefox in terminal gives me "Segmentation Fault." Same is true for Totem.
When I run Firefox as root ("sudo firefox") then it works. Same with Totem. But that's quite annoying on all sorts of levels! I've tried completely removing firefox, deleting .mozilla from home directory, then reinstalling. Same problem.
When I launch Amarok, that crashes immediately with a signal 11 (SIGSEGV) fault. When I run as root (via terminal) it does start, with various error messages on display.
This is all quite recent, maybe a week or so ago. I have all the updates (levels 1-3) from mintUpdate, and I recently marked all upgrades in Synaptic to give that a try (it upgraded the kernel) but again this hasn't solved anything.
(Mint 7, Gnome)
Help would be appreciated before I start thinking about a fresh install