@tofu @theogrin @mcc folks already are. On desktops Waterfox and Librewolf for those wanting to stick with the gecko rendering engine. Only Waterfox is available on Android though.
Both of these forks have existed well before Mozilla decided AI was a better feature to add than bug fixes. Waterfox has been around for ages; it started life as a 64 bit compiled version of Firefox when Mozilla was still only doing 32 bit. It's had its ups and downs, but they have made a strong #NoAI statement and are on solid ethical ground now.
If you want AI free Chromium browsers, try Ungoogled Chromium, Helium, and Vivaldi. Only Vivaldi is also on Android, and they're pretty open about their contempt for AI (if not so open about their source code).
https://www.waterfox.com