[Gankro]

even more clearly:

webrender is "the stuff that works pretty ok and we can run through CI". In principle enabling webrender should get you the ~same results as not having it on, visually, modulo a few known bugs.

webrendest is "everything we're working on, no matter how broken"

It's a pretty big project so there's lots of stuff in tree that's barely functional (especially true with the layers-free pivot).