My trouble started with my update from firefox-39 to firefox-40 back in August 2015. At first the update seemed absolutely benign and I noticed nothing bad happening.
Slowly but surely firefox has been driving me crazy by doing little things that are merely annoying. Today firefox did something so outrageous that finally I had to stop and fix the problem. The big change AFAICT was the switch from sqlite to json for storing data in your ~/.mozilla directory. Today I noticed that dozens of files in my ~/.mozilla directory had identical date and time stamps from back in August, all apparently written by firefox-39. The problem is that firefox-42 still reads *some* of those old files for backward compatibility, but apparently not all of them. Anyway, one obvious thing to do is start with a fresh ~/.mozilla directory when you use firefox-42. Or at least make a complete copy of your existing ~/.mozilla so you can start over when you have trouble. I recommend that you *not* use the profile editor from firefox-42 to edit any old firefox profiles you may have. You run the risk of damaging or deleting your old profiles by doing this. This is *not* equivalent to backing up your ~/.mozilla directory. Others have already learned the hard way, including moi.
