Mozilla owns the Firefox trademark so if they get to choose how the trademark is used. I remember that a while back Mozilla threatened. I can't remember if it was Debian or Linux Mint who received the threat.

[–] kbal@fedia.io 1 points 5 days ago

Oh yeah, I remember debian's Firefox used to be called something else for trademark reasons some years ago. I wonder how much linux market share firefox lost as a result. Not sure what changed, I guess in that case Mozilla must've come to their senses. I was mostly an ubuntu user in those days.

... lwn has the story: https://lwn.net/Articles/676799/