Am i joking or what?
No, FF crashes, a few times on me recently. You'll see what had caused that by opening up your Windows Task Manager and look for "Mem Usage" under "Processes" tab.
Firefox eats up a lot of memory, it's also called memory leak, if you has many tabs open up and downloaded a lot. Review this from the knowledge base and it can easily be fixed, normally, good luck to you.
I use IE7 beta with FF concurrently most of the time. It's noticeable that when IE7 is minimized it uses a lot less memory (could be just 10%, I have seen few cases). FF doesn't have this trick therefore if your PC/notebook is lack of physical memory you may have to restart firefox from time to time to get rid of piled up memory usage.