We currently support macOS versions 10.9 to 10.15. We're looking at moving users on versions < 10.12 to the esr branch with the release of Firefox 78, to both be able to support them for about a year longer, and reduce the burden from old versions on engineering and QA for mainline Firefox.

Bugbug thinks this bug should belong to this component, but please revert this change in case of error.

This is pretty appealing to me but how does this timeline line up with Chrome's plans? They currently support 10.10. Dropping 19% of our mac users feels like a lot...

Have we got some logic in here to accommodate people who could update their OS, but update their browser first? I don't know how many people might be affected by it - maybe we want to find out? - but if we win the update race with the OS we might be trapping people on ESR who don't need to be there.

It makes sense to drop support for macOS 10.9 and 10.10, as there is very few reasons to stay on 10.9 (old macOS design) and 10.10 (SIP not present). but there is no point to drop support for macOS 10.11 considering it is the last version of macOS without SSE4.1 requierement, there are much computers stuck in this version officially and unofficially.