If I disable CALL ROP Gadget detection (32 bit) AND (64 bit), if I also disable RET ROP Gadget detection (32 bit) AND (64 bit) in the Browsers column of the Anti-Exploit Settings of Malwarebytes, then FF will start and run as expected. However, I am not comfortable with this solution and will not use it going forward. Seems like something is happening in FF to make Malwarebytes shut it down. As far as I'm concerned, that's why I pay for Malwarebytes. So what is going on with FF.

I did a complete un-install, following your directions. I DID keep my preferences, but checking before a new installation, FF was removed completely. Currently running ver 58, or whatever is the latest as of Jan 23, 2018 from your site. The installer I downloaded is version 4.42.