Hi, your Firefox said it is version 78 running on Mac OS X 10.11. If that is your correct Mac OS version, then you have the latest Firefox available for your OS. '''''Have you considered upgrading your Mac?''''' If you can install macOS 10.12 "Sierra" or later, then you can use the Extended Support Release of Firefox 115, which is still supported with security updates for at least a few month months. I don't know what will work on your hardware, but if you visit the Mac App Store in Safari, you might be able to find a newer version that will work. ---- If that is not possible and you want your Firefox to be able to run add-ons, let us know and we can continue the discussion on that topic.