how do i update and install

It appears you are running the old EOL macOS 10.11. The most current version of Firefox you can run on macOS 10.11 is the Firefox 78.15.0esr you appear to have used topost this thread with. https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr If you can update your macOS to 10.12, 10.13, 10.14 then you can run a more current version of Firefox which is Firefox 115.33.0esr based on the Firefox 115 Release. https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support