Why don't you get some c/c++ grizzled veterans on your team and fix the memory leaks that have dogged FireFox ever since the beginning?
It's not plugins or extensions. This is a problem that never goes away. Memory usage creeps up into the multiple GBs (I have 12 GB of ram, the more you give the more it takes), and eventually the little OOPS Firefox crashed dialog is the only thing running. What about reviving the Electrolysis project for multi-process operation? In modern versions of IE and Chrome, this capability is so useful to kill off offending tabs.
Electrolysis is alive and well, and is currently hot on track for a future release. Please note that Electrolysis (or per-tab process) doesn't improve memory usage (In fact Chrome has significantly worse memory usage than Firefox because of it). One thing we are trying to do right is make sure we don't worsen memory usage because of Electrolysis.
Memory usage is something that's difficult to work on with little information, so if you want help please provide us some more data such as your about:support (type it in your url bar and press enter) and your about:memory (same)