Oh, I don't know, maybe breaking literally all of their extension with the deprecation of XUL?
I'm a happy firefox user, and I'm pretty sure it was the right choice IMO, as firefox is certainly much more stable and fast now than it was before. But it was certainly a very, very rough process and left some very popular extensions broken without alternatives for months and even years before the necessary APIs were added to webextensions to bring them back.
"Breaking all of their extensions with the depreciation of XUL" is one interpretation, another one is that it was needed (of course it was the correct choice!) and there wasn't going to be an easier approach than just ripping the band-aid off. It needed to be done, it's done, and now instead of discussing the larger picture, we're talking about XUL depreciation from Firefox which happened in 2018. So what's your point?
