On that date, users of Firefox still running OS X 10.9 (Mavericks), 10.10 (Yosemite) and 10.11 (El Capitan) on their Macs will instead be shunted to the extended channel and given 78.0 ESR.

The move, a first step towards dropping all support, will take place June 30, when Mozilla releases Firefox 78. Mozilla this week announced it would automatically move users running outdated versions of macOS to the Firefox Extended Support Release (ESR), an edition that provides security updates only.