+++ This bug was initially created as a clone of Bug #1637533 +++

We're looking at moving users on versions 10.12, 10.13, and 10.14 to the esr branch with the release of Firefox 115, 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.

I believe it is too early to stop supporting macOS 10.13 High Sierra and macOS 10.14 Mojave. The reason is in the support of 32-bit software: macOS Catalina dropped support for 32-bit applications and plug-ins entirely which made a lot of software broken and even unusable, including OpenCL data corruption and problems with saving files to exFAT formatted drives. Furthermore, StatCounter shows that there are still 1.62% of users on macOS High Sierra and 1.62% of users on macOS Mojave. Because of these reasons, it is reasonable to extend the support of macOS 10.13 High Sierra and macOS 10.14 Mojave at least until the next ESR release.

Users who still use macOS 10.13 High Sierra or macOS 10.14 Mojave are likely people who still face various software problems in macOS Catalina and later versions where the support of 32-bit software is removed, and updating the macOS version is not an option for them. That is why there is a need to extend the support for macOS 10.13 High Sierra and macOS 10.14 Mojave to serve these specific people.

(In reply to macOS User from comment #1)

I believe it is too early to stop supporting macOS 10.13 High Sierra and macOS 10.14 Mojave.

10.13 and 10.14 users will still be able to use Firefox ESR 115.