What do you see here? https://support.mozilla.org/en-US/kb/see-active-policies-firefox-enterprise

Also, try downloading another copy of Firefox and run it from the folder. It's good to have a separate version for testing these kinds of issues. https://www.mozilla.org/en-US/firefox/all/#product-desktop-release

Mozilla only provides internal Firefox updates for the official builds of desktop Firefox (for Linux, Windows and macOS) from https://www.mozilla.org/firefox/all/

Third-party builds like those installed from a package repository for a Linux distro do not get internal Firefox updates.

In this case it looks like you have Firefox from the Mozilla server and a version from the Linux distro and that updates have been disabled by a system wide policy or autoconfig file. The about:policies page should confirm that a policy that disables updates is active.

• https://github.com/mozilla/policy-templates

This is mentioned in a recent Mint blog post:

https://blog.linuxmint.com/?p=4244