Every couple of months I will start up my computer and find all my settings have changed and my Firefox add-ons are gone. I was not able to discern why but I made some changes in the configuration and got the text size back to what I wanted. This time it happened none of those configurations changed but I still had changed text size. I refreshed Firefox and found my add-ons immediately were reinstalled even though they were shown to be working when I checked my browser settings. One of the add-ons was Yahoo Mail ad blocker. I have used Yahoo Mail for years. Recently they have tried to make changes in my mail display to where I am being forced to go ad-free and upgrade to a mail subscription. After this most recent challenge to my computer setting, I am beginning to think Yahoo is disabling the Yahoo Ad Mail Blocker to get me to go to their subscription. Either that or Microsoft is challenging me to use their browser. It is like their is a war going on to win the internet. I miss the old Internet. Is there anything that can be done so my settings don't get hijacked?
It sounds like Firefox is creating a new profile, or resetting itself.
Type about:profiles<enter> in the address bar. How many profiles are listed? How many should be there? Also, open the profile folder in your file explorer.
Look on your desktop. Do you see a folder called; Old Firefox? Look inside. Look for the folder with the latest creation date.