While I haven't had Firefox totally freeze to the point of requiring a reboot, I did notice in recent versions (which could go back to 5) where page navigation would often grind to a near halt on my Desktop. A workaround I'm using is by disabling Hardware Acceleration and so far this issue hasn't reoccurred for me. This article shows how to disable Direct2D Hardware Acceleration in Firefox.
On the other hand, this hardware acceleration issue also occurs in Mozilla Thunderbird and so far I haven't found a way to disable it in that application. While it doesn't have much CPU usage, it hogs my graphics card to the point where I cannot watch video unless I close out of Thunderbird.