Not a priority or anything, but reporting as it is an unusual behavior that I haven’t run into before and the circumstances are interesting!
When my computer restarts the setting for Compact UI resets to Not Compact - Expand Images. It doesn’t look like any other settings change, just that one setting for images. I like More Compact - only thumbnails so I have to change it back each time my computer restarts which isn’t common but often enough that I’m confident in the pattern.
It doesn’t seem to happen just from closing the browser and reopening it or from logging out and back in again, just when the computer restarts. Using LibreWolf on a Windows PC.