Igalia is the real deal. Many companies that want bugs fixed or features added to web browsers hire Igalia to make those changes. They also maintain WebKit on Linux (gtk and wpe) https://planet.igalia.com/webkit/
I've been looking for a while for Linux distro that's easy to build from scratch and customizable.
Every now and then you run into these small-ish expert consultancies that actually are the force behind a lot of open source.
They seem awesome.
The technical talent at Igalia runs deep.