Momiji playing YouTube on an older Mac, with its About window alongside. An early 140.1 build, from the project’s README.

Momiji is a one-person backport of Firefox for 64-bit Intel Macs running OS X 10.7 Lion through macOS 10.14 Mojave. It’s for the Mac that still works fine and the browsers that stopped caring.

Browsers drop old macOS versions on a schedule. Mozilla’s Firefox 115 release notes call it the last major version for macOS 10.12, 10.13 and 10.14; users there were moved to the ESR 115 line for security fixes. Chrome 116, from August 2023, was the last release for 10.13 and 10.14. A Mac of the Core 2 Duo era or later can run for years after that, on a browser frozen in 2023.

Momiji’s answer is a rebuild of current Firefox code for those systems. Its base is Firefox 140 ESR, and the README calls it the successor to Firefox Dynasty, the earlier legacy-Mac Firefox project, with debloating patches borrowed from LibreWolf and GNU IceCat. The name is 紅葉, “red autumn leaves,” and the icon is a maple leaf. The crash reporter is stripped out.

There are two channels. Stable follows Firefox ESR: 140.17.0 landed on October 4 with Mozilla’s security fixes, and it is the last build on the 140 base; the next switches to ESR 153. Rolling tracks Firefox’s regular releases (156.0 in September) and reports itself to websites as macOS 10.15. Each release ships as two zips, one for 10.7–10.11 with a compatibility shim and one for 10.12–10.14, both built for Conroe/Merom-class 64-bit Intel chips and newer. Rolling and Stable share a profile directory, so back up before switching.

The caveats are real. This is unofficial, built by one maintainer and not affiliated with Mozilla; the source is public, but you are trusting that person’s binaries with your browsing. Netflix and Spotify don’t play by default because Widevine isn’t supported (the README points to a downloader by Wowfunhappy as a workaround). Hardware acceleration can misbehave: pre-2010 machines may crash with SIGILL until you start in safe mode, and Discord voice and video need a newer Firefox than 140. It is MPL 2.0 licensed and free.