Not at all. Personally I like to have a shared data partition for my media files. Both OSes can use that just fine, if it’s NTFS or exFAT formatted.

I would say no. With the recent debacle the writing is on the wall. Mozilla is not taking our privacy seriously. So, I have switched away from vanilla Firefox.

I would recommend using a fork instead: LibreWolf, or Floorp, or Zen; and Ironfox on Android. Mullvad Browser is another option.