prime video asked to update to firefox mozilla in order to watch their videos, but still not working

It appears you are using the old EOL macOS 10.13 as the most current Firefox you can run on macOS 10.12, 10.13, 10.14 is Firefox 115 ESR which is currently at Fx 115.32.1 esr and last planned update will be Fx 115.33.0 esr on Feb 24. https://support.mozilla.org/en-US/kb/firefox-users-macos-1012-1013-1014-moving-to-extended-support Firefox 116.0 and later including the Fx 140.7.1 esr and Fx 147.0.4 release requires macOS 10.15 (ten.fifteen) or later to run. So unless you can update your macOS to 10.15 or later the most current Firefox you can run is the Fx 115.32.1 ESR you are currently using