You you can still use Firefox 115 ESR, just may be more and more vulnerable as time goes on along with having issues on some sites due to using a older version of Firefox as site may be expecting newer Firefox versions.

The Firefox 115 ESR is based on the Firefox 115 released back on July 4, 2023 but with allowed stability and security fixes since. The ESR channel builds are normally made for Enterprise users in mind who like longer term stability over the rapid release. The Fx 115 ESR became an option for the EOL Windows 7, 8, 8.1 and macOS 10.12, 10.13, 10.14 OS users to use for a while like Mozilla did with Fx 52 ESR and WinXP/Vista for a short while.

The last planned Firefox 115 ESR update is Fx 115.33.0esr in February 2026 unless Mozilla decides to extend updates for a fourth time.

A way to use more current versions of Firefox on that system may be to install a Linux distro. I do suggest perhaps looking at a extended support distro version and using the Firefox Linux tarballs from Mozilla to continue getting internal Firefox updates from Mozilla (make sure Firefox folder has read/write permissions for the user) even after when that version of Linux distro is made EOL in package updates.

Hello

To complement, this discussion.

Maybe, because the reason:

https://connect.mozilla.org/t5/discussions/windows-7-support-with-firefox-esr-115-x/m-p/100234/highlight/true#M38960

https://support.mozilla.org/en-US/questions/1522469

Thing is pretty much every other web browser is based on Chromium or even a third-party fork of Firefox. Chromium 109 in January 2023 was the last to still support the EOL Windows 7, 8, 8.1 so be glad Mozilla is still even providing updates for the old Firefox 115 ESR till Fx 115.33.0esr in February 2026. The Firefox 115 ESR was originally planned to end as of Fx 115.15.0esr back on September 3, 2024.