Short answer: No.

Long answer: Unless the button says "phone home my information to Mozilla", this license wouldn't cover that. This license only covers whatever is necessary to make the button itself work - whatever is necessary to realize the user's intent.

They didn't need a license to your data before. Why should they need it now?

From the link that was already provided, and which is repeated in their Privacy FAQ: "Since we strive for transparency, and the LEGAL definition of “sale of data“ is extremely broad in some places, we’ve had to step back from making the definitive statements you know and love."

That seems like a pretty reasonable justification to me

Nope. It seems like legalspeak to say "we sell your data" while making it sound like they don't.

Let me guess: chmod775 will not reply to this comment.

It's an apt username for naively giving read access

See my reply to you here: https://news.ycombinator.com/item?id=43205587

Honestly I'm surprised that a research technician is more interested in this style of "argument" rather than figuring out the meaning of a (very precisely worded) sentence to for its own sake.

That'd be a matter for the privacy policy. The section in question is whether they can then go ahead and publish a list of all the buttons you pressed. Which according to this license grant they can, but only if it "helps you navigate, experience, [or] interact with online content as you indicate with your use of Firefox". What does that mean? I have no clue. It's a really strange restriction and I can't decide if that's wide open or so narrow that it is basically never met