Emilio Cobos Álvarez:

So this week I landed a few patches that completely removed XUL layout from the Firefox codebase.

This means that (modulo a few exceptions documented below) all the Firefox UI is using regular web technology to render (mostly CSS flexbox).

This was a rather big effort (first filed 9 years ago in bug 1033225), and I wanted to document some of the things that I learned during the process, some of the things and decisions that made it possible, and some of the things that I would’ve maybe done differently.