They also killed off Live Bookmarks. I used that for years in FF and then later Waterfox until the PrivacyOne buyout, now I have to open a separate program to read my rss (rssowlnix)
Live Bookmarks died because it was ancient code that needed to be rewritten, but most people didn't use the feature. Mozilla added telemetry to analyze feed usage and the results came back with less than 1%. It was about resource allocation for development and no volunteers came forward.