Have you noticed any tangible benefit to using a 64-bit build over a 32-bit one? Performance of the current x64 builds as measured by responsiveness and javascript benchmarks is about on-par with the 32-bit version for most things; the performance and even compilation of plugins is however another matter entirely and the reason for using Firefox for me over another solution is almost always the plugins available.

I have been using PaleMoon builds and from what I gather the source tree is not being tombstoned, just the nightly builds. [0]

The reasons given for crashes (driver/component out-of-tree bugs) make sense but I'm not really involved in the development or testing so I'm sure others will have better input.

[0] http://forum.palemoon.org/viewtopic.php?f=15&t=1700