Continuing the discussion from Does anyone know what happened to Firefox Dynasty?:
Thanks to one person who forked the Firefox Dynasty sources before the site was taken down, another developer in the community was able to resume work.
The result is the Momiji web browser. This continues the Firefox Dynasty work, making modern versions of Firefox available to users running macOS 10.7 through 10.14.
The latest release is based on the Firefox 140.2.0esr release, so it’s still a bit behind the official releases (the latest ESR release is 140.9).