(The F-Droid branch at least) will "shim" the trackers, meaning rather than attempting to dive into the code of every single update and remove all the tracking hooks, it instead replaces the tracking code with blank functions that don't do anything but exist just so there is something there when Firefox attempts to call into them so it doesn't crash.

Naive scanners that simply read the list of classes that are in the program will see them and go "ooh there's a tracker here", but they can't distinguish between actual tracking code and these "neutered" versions that don't do anything.

I am not certain, but Mull still has functionality with FireFox sync, which might be a reason why it has a tracker.

Tor is a special case. They leave some stuff in tact because the average Firefox user would never touch that stuff and it would key tracking companies in MORE that the tracking stuff is disabled. Its called finger printing and part of what Tor tries to do is make everyone's fingerprints as innocuous as possible