FireFox most definitely has Memory Leaks. Always has.
I often have to just close it down and reopen it.
I also try not to have more then 50 tabs opened, but I don't succeed much there. Last one way 157 tabs
At present I am on ver 31. I just stopped the Auto UpDate and only update when I want to now. This seemed to fix the problem of Working and then Not working and then working again.
I would love a simple browser that just Worked, with TABs of course.
I might have to look into SeaMonkey also.
Sometimes I do go back to an earlier Ver of FF that I know works with out problems BUT that is way back to something like Ver 19 LOL