Questions about Firefox Privacy and Security

Hello, I have some questions about the security, privacy and generall usabillity of Firefox:

  1. If you change the zoom level of a website (like from 100% to 90%), can the website then use this information to track you or does this make you more fingerprintable?
  2. Is it possible to use custom Firefox CSS themes like Firefox-UI-Fix or Firefox GNOME Theme without compromising privacy or security?
  3. What is the best and easiest way to reset a profile without creating another profile, if there is even one?
  4. If you use a density setting like “compact”, does it make you more fingerprintable?

Answers would be pretty helpful for me!