I abandoned Firefox because it was dragging its feet on some vital web standards such as WebGPU and import maps. The former is obvious. The latter is such a massive quality of life improvement for devs (makes build systems obsolete) that I simply could no longer care for Firefox which ignored it for the longest time.

That's literally the process. TC39 in particular requires two real world implementations to exist before some new feature becomes a formalized part of the standards.

Several proposals backed by "the primary competitor" failed to get through the process, or were radically changed to make other implementors happy.

Mozilla is a founder of WHATWG and they have, historically, had opinionated takes on standards.

https://mozilla.github.io/standards-positions