Because some project manager had "AI" on his performance goals this year.
Firefox is buggy as hell - which is incomprehensible given its age, but older brother Netscape had the same problem 20-ish years ago. The Netscape 4.x days were absolute hell and you could go hardly a day without the browser crashing.
Despite this, it's packed with nonsense no one asked for like Pocket. Which is a coincidence because "AI assistant for Firefox" is the dictionary definition for redundant things no one asked for, with better alternatives preexisting.
At this point Firefox needs to die and something new and manageable - with energetic developers - needs to take its place. Maybe Microsoft could open source the original Edge engine? The one before they bent over for the long dick of Google Chrome.