Have you seen this: Last Updated: Mar 28, 2026

https://linuxvox.com/blog/update-firefox-linux-mint/

Mint 18.2 is old and even though it was a LTS version, support including software package updates ended back on April 2021.

You appear to be using the old Ubuntu package build of Firefox 88.0 which was likely the last Firefox package update provided for the old Mint 18.2 users as Mozilla released Fx 88.0 back on April 19, 2021.

The two ways to have a newer version of Firefox is to either update to a currently supported version of Mint or use the Firefox Linux tarballs from Mozilla. At least with the tarball version you can get internal Firefox updates from Mozilla in the way macOS and Windows versions do. Though make sure the Firefox folder has read/write permissions for the user to get updates as a easy way is to have folder in Home..

https://www.firefox.com/download/all/

A note, if you have older hardware with a 32-bit CPU then 32-bit Linux support has been dropped as of Firefox 145.0 and later. You can use the Firefox 140 ESR for now to get security/stability fixes though the last update will be Fx 140.15.0esr in September. https://support.mozilla.org/en-US/kb/firefox-has-ended-support-32-bit-linux