Are you currently stuck with the Firefox 121 version from Ubuntu?

If you run the latest or a recent version of Ubuntu then you should be fine with the current release. If your Ubuntu version has reached EOL and you can no longer your distro's version, then you can install Firefox from the Mozilla server.

• https://www.mozilla.org/en-US/firefox/148.0.2/system-requirements/
• https://www.mozilla.org/en-US/firefox/all/desktop-release/

• https://support.mozilla.org/en-US/kb/install-firefox-linux

That is a downside of using package builds of Firefox provided by Linux distro package manager as once that version of Linux distro you are using is EOL in software updates you will then be stuck with a old version of Firefox such as the Fx 121.0. You would need to update to a current version of Linux distro to get new Firefox package updates..

Though as suggested you can use the Firefox Linux tarballs from Mozilla as it will get internal updates from Mozilla like the macOS and Windows versions from Mozilla do. You just need to make sure the Firefox folder has read/write permissions for the user to get the updates. If you are the only user then a easy way is to put the Firefox folder in Home.