Sometimes Firefox is set to run in Compatibility mode for an older version of Windows. This almost never solves a problem, so try undoing that with the following method:

Close out of Firefox.

Right-click the desktop shortcut for Firefox and click Properties. If the shortcut is pinned to the taskbar, you have to right-click twice: once on the Firefox Taskbar button and once on Firefox on the context menu. It can be weirdly slow.

In the Properties dialog, change to the Compatibility tab.

If anything is selected in the Compatibility mode box, turn it off, you want it to run as a Windows 10 application.

If anything is checked under Settings, uncheck it.

Then click OK and start Firefox again.

Can you update now?

I guess I should mention that the current ESR release is based on Firefox 128. If yours doesn't automatically jump to 128, you can download from here:

https://www.mozilla.org/en-US/firefox/all/desktop-esr/

Your UserAgent in more system details on right shows you used the UA of Mozilla/5.0 (Windows NT 6.2; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0 to post this thread.

The NT 6.2 is for Windows 8 which is why you have Firefox 115 ESR.

Firefox 116.0 and later requires Windows 10, 11 to run so if you were to download Firefox from mozilla.org now without fixing the UA, you would get served the current Fx 115.18.0esr as the site will think you have Windows 8.

I agree with above that you are likely running Firefox in Windows 8 compatibility mode on Windows 10 for some reason. If that is not the cause then see https://support.mozilla.org/en-US/kb/how-reset-default-user-agent-firefox