I have been running MOOX's optimized Firefox build for a month now and I must say they are sure worth a look. They indeed run faster than original builds as the site author promises and I had less Firefox crashed with those than with the original builds. I don't have the explanation, so don't bother asking.
At work I run M3 version and at home I run M2. Both run just fine, just don't try to run M3 build on a M2 machine.
I also tried bleeding edge trunk builds, but I gave up. Those are not stable and just don't work like they should. I had some trouble with crashes and Tabbrowser Extensions didn't work OK with some version didn't work at all.