Personally, I'm just sick and tired of modern UI design. Bring back density, put more information on the screen, eliminate the whitespace, use simple (and native!) widgets, get rid of those fucking sticky headers, and so on.
In addition to all the software freedom stuff, and so on. Also, I wish GPL were more popular too.
Yeah, the biggest problem with Firefox is that its engine is so hard to embed. Chrome has endless clones because it's just so damn easy to embed. And Firefox just has some weak forks like Librewolf.
I'd really rather see Mozilla focus on this rather than all their other stupid endeavors....