I have been to your website to download Firefox on my IMAC 10.10.5 and every time I complete the download I get the message that the version will only work on IMAC 10.12. I specify 10.10.5 it does no good. You are answering that no one has this problem. You have not answered the question.

Firefox 78.15.0 ESR was the last version that supported the old EOL Mac OS X 10.9, 10.10, 10.11 as Firefox 79.0 and later including the current Releases has required Mac OSX 10.12 at minimum to run.

You can download the old Firefox 78.15.0 ESR from https://archive.mozilla.org/pub/firefox/releases/78.15.0esr/mac/en-US/

other locales are at https://archive.mozilla.org/pub/firefox/releases/78.15.0esr/mac/

https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr