Yeah these are definitely slop. The angles in the mirror reflection make no sense. The corner edge of the reflected wall wouldn’t be perfectly parallel to the frame of the mirror since the mirror is standing at an angle. The way it is now would only make sense if it was painted on or if the mirror itself was exactly perpendicular to the floor.
Firefox, its logo, etc are trademarked and therefore restrictions apply when re-distributing, and that has been the case for as long as I remember. There’s nothing stopping you from compiling it yourself, calling it Firefox, or using their branding, as long as you don’t redistribute your build and modifications to others while still using their branding.