They still have not fixed their build system. Meson/ninja or cmake would be alternatives. Nothing to have them abandon mozconfig ... this is legacy code. The rest of the world moved on. Mozilla lives in the past.
FWIW the Firefox build instructions [1] look a lot saner to me than the Chromium build instructions [2].
[1] https://firefox-source-docs.mozilla.org/setup/linux_build.ht...
[2] https://chromium.googlesource.com/chromium/src/+/main/docs/l...
And one would hope they stay there, because all the newer stuff is far more user-hostile.