Signing certificates used in addons/browsers have some expiration time, so they need to be updated regularly.
For example, from the release notes of Firefox ESR 115.13.0:
The root certificate used to verify add-ons and signed content has been renewed to avoid upcoming expiration.
Also, old addons had to be re-signed recently:
Note that using old browser without security fixes is super dangerous, even in Linux.
See for example bugs from Pwn2own event:
https://www.bleepingcomputer.com/news/security/mozilla-fixes-two-firefox-zero-day-bugs-exploited-at-pwn2own/
An attacker was able to inject an event handler into a privileged object that would allow arbitrary JavaScript execution in the parent process.