While Firefox is not exactly super crash-prone, I noticed over the last 2-3 years that it has a nasty habit of gobbling up memory. When I run my machine non-stop over the weekend, it is totally normal for it to eventually reach about 1.5 GB of memory usage (no matter how many tabs I have open at that point) and then strange things happen - like graphics not loading correctly, GUI elements not showing up anymore, web pages freezing etc. So I can totally understand it if people who use Firefox more than me, e.g. at work, have problems at least once a day. It is simply not stable under heavy usage.