So out of the blue I was able to get FireFox 58.0.2 running on a 2007 MacBook Pro with Mountain Lion. Thinking something may have changed between 57 and 58 I went and tried to get it working on my other Mountain Lion machines. No luck. Every last one of them crashes at startup. So the question is, what is making FF Quantum work on SOME machines and crash upon startup for others? The ONLY difference between the one system that has FF 58 working and the ones that don't is the graphics card. Any reason to think that could actually be the problem? GMA950 vs Radeon X1600?