Happening since last up date. Using FireFox 56.0 Mac OS 10.12.6
This is the simples option, not always help but we encourage to try.
- Copy and paste in address bar about:support - Select following http://nimb.ws/Vm5pjy - Rename this folder to any name and restart Firefox http://nimb.ws/awxfuW BUT don't delete it. Just rename.
If it won't help, let us know.
Also, if you don't see welcome message but settings get rest, that will be fixed next update soon.
Customer support service by UserEcho