Literally every other browser and most tech companies are shoving AI down users throats. Firefox isn't missing the boat by neglecting AI, they're missing it by being an alternative which reminds us how nice things can be without it.
The past 15 years has been a slow decline while they were trying to prove some relevancy outside of their core product. With mobile browsers being locked down a decline was going to happen anyways but if they stuck to their guns at least they wouldn't have wasted a bunch of money and maintained more of their base.
Who knows, their position sucks, but they're not going to win anyone by being the worst AI focused browser which happens to have an off switch.