For the old eol macOS 10.9, 10.10, 10.11 the most current Firefox you can run is Firefox 78.15.0esr which you may have. https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr

Firefox 79.0 to 115 ESR requires macOS 10.12, 10.13, 10.14 to run. Firefox 116 to current requires macOS 10.15 or later to run. The older Firefox 115 ESR is still being supported with updates as it is currently at Fx 115.18.0esr and will be updated til at least Fx 115.21.0esr in March 2025 unless Mozilla decides in early 2025 to extend updates again. https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support

So unless you can update your macOS to at least 10.12 you are pretty much stuck with Fx 78.15.0esr as the most current you can run.

Thank you very much, James, for your quick reply. This certainly doesn't solve my problem but it answers my query. I'm not going to throw away my perfectly fine computer for the sake of consumerism. Soooo... I guess future will tell what happens. I really hope I can continue using Firefox. It's my favorite browser at this point.