Check to ensure your Mac accepts the reader.For example, it might say that your Mac doesn't have enough free storage space for the installation, or that the installer is too old. If a macOS installer can't be used on your Mac, the installer will let you know. Mozilla plans to end support for Mac OS 10.9 to 10.11 (Mac OS X Mavericks, Yosemite, and El Capitan) next year Firefox Stable installations on these systems will be migrated to Firefox ESR 78 when the new version is released on June 30, 2020. The release of Firefox 78 and Firefox ESR 78 changes that.
