2) Users are justifiably concerned.
3) Mozilla explains that the add-on is actually anodyne; the developers responsible were having fun with an opt-in research service.
4) Some users try to justify their initial overreaction by painting Firefox as mysterious, dangerous entity, fabulating conspiracy theories about one of the most forthright and open OSS companies in the world.
Really, guys. If Mozilla was hellbent on invading your privacy, do you really think they would proudly entitle their tracker "Looking Glass". Or would they call it debugservice_1223?