you will have to search. its hidden in unrelated commits. but features that were removed at different points in time are: no referrer/only first party referrer

you will have to search. its hidden in unrelated commits. but features that were removed at different points in time are: no referrer/only first party referrer in settings. no referrer in their about:config equivalent at the time (its a moving target). command line option to disable referrer. all added and vanished at random points in time.