Doesn’t matter if it’s the sites that are the problem, Firefox has lost momentum to such a degree that sites don’t care anymore. So they should tread carefully with features like this.
Using Firefox in its default configuration shouldn't break websites.
Firefox taking a hard nose approach here makes it impossible to use this on parents / grandparents computers to help keep them safe.
I don’t mind losing Twitter… but I can’t speak for others in my family. Just sucks. But on popular sites that run blockers, there should be like a little pop-up that says, “Give me access, and let this dumpster fire burn.”
So even when they still had a considerable market share, these kind of stances may actually be detrimental to their user base.