Is this behavior expected? I would imagine it would be a privacy violation in a multi-user system. I thought they had some sort of encryption for hiding the sites that I visit.
BTW, FF does not do this on private mode. But still it is concerning, that any program can know about the sites I visit just by looking at ~/.mozilla/profile/storage/default.
If you are worried about other users on your machine then you can verify/update your umask so others can’t access your files.
If you are worried about programs under same user then you need to use AppArmor and or firejail heck you can even go crazy and use SELinux.