Firefox the latest version of Firefox is 129.0.1.

You can get it from here: https://www.mozilla.org/en-GB/firefox/download/thanks/

That will come as a .tar.bz2 archive. Open that and you'll find a directory called firefox. Put that somewhere of your choosing. Now click into it and click firefox to launch it. You can also do it from a terminal by typing <WhereYouPutIt>/firefox/firefox, eg ~/temp/firefox/firefox

A better, but more complex, way is to set it up to use your normal package installation system, see: https://support.mozilla.org/en-US/kb/install-firefox-linux#w_install-firefox-deb-package-for-debian-based-distributions

edit: fixed second link

If the current version doesn't work, find another here. https://ftp.mozilla.org/pub/firefox/releases/ Download, unzip, and run firefox-bin from the folder and see if you have the same issue.

Note only the official Linux tarball .tar.bz2 builds from Mozilla like say https://www.mozilla.org/firefox/all/#product-desktop-release gets internal Firefox updates from Mozilla. You need to make sure this extracted Firefox folder has read/write permissions for the user as a easy way is to have the Firefox folder in Home

The Firefox package builds like deb, snap, flatpak, rpm are updated in the package repository manager.