I've never understood the argument. It seems to have kind of been collectively hallucinated into existence by waves of internet comment sections over the years. But these aren't mutually exclusive, and nobody has made a case that the resources for these other features are compromising the ability to deliver core browser functionality.

They also seem to assume that it's development decisions, rather than Google leveraging its search dominance and financial muscle, that are tied to changes in market share. I actually think these value-adds can be good, can punch above their weight and can, if they are smart in picking their spots, do so without necessarily compromising their ability to advance the development of Firefox.

And nobody ever stops, breathes in and out, collects the evidence and makes the actual case. It's just kind of assumed, asserted, repeated, assumed again, repeated again ad nauseum. Because enough people have seen other people say it, so they say it too knowing it leads to upvotes.

The ones closest to citing evidence, thankfully understanding at least how a real argument would actually work, are also the most unhinged, which probably isn't a coincidence.