The thing is, I really don't think, Google would care about Firefox. Firefox is sitting at negligible percentages of usage share. The only real competitor to Chrome is Safari and that's because of iOS.
I guess, they might impact Safari on macOS with this, but someone would have to try this out to actually see, and ultimately, this could still just be a dumb mistake.
Having said that, Google holds a near-monopoly in both video content and web browsers. They have a special duty to not disadvantage competitors and even if this was an honest mistake, I do think, it deserves a slap on the wrist.
They do have a history of such things happening, yes, which is why my comment exists in the first place. Normally, I would assume this to just be the result of regular shitty management practices paired with regular shitty profit motives.
The history makes it look like they might genuinely have a higher motive here, and I'm saying I still don't think so, because it would be far too petty and I don't see them benefitting that much from it.