They do deliberately slow their sites on Firefox, as has been discussed in many past hn articles. YouTube for example. Pardon my lack of references, you should confirm for yourself with a hn search in case I am mistaken
For me, this is blatant anti-competitive practice and should be punished.
All just speculation, but I haven't noticed the same issue.
It's since been fixed.
Is that consistent with the "it is because FF doesn't support new thing yet" explanation?
It is not the case.
But who would have the legitimate right to stop it? Do we want government dictating product features?