Windows server 2012 R2 is on same NT 6.3 as Windows 8.1 https://support.mozilla.org/en-US/kb/firefox-users-windows-7-8-and-81-moving-extended-support Firefox 116.0 and later requires Windows 10 or later and Windows Server 2016 or later to run. Operating Systems (32-bit and 64-bit) Windows 10 or later https://www.mozilla.org/firefox/116.0/system-requirements/ https://www.mozilla.org/firefox/128.0esr/system-requirements/ https://www.mozilla.org/firefox/130.0/system-requirements/ Firefox 115.15.0esr is up to date as it came out at same time as Fx 128.2.0esr and Fx 130.0 release. Unless Mozilla decides before October to continue with updates then yes the older Firefox 115 ESR will be made EOL in October. Pretty much every other major web browser (using Chrome or Chromium) already dropped support of the EOL Windows 7, 8, 8.1 back in Jan/Feb of 2023. For Firefox 115 ESR users if they are running Windows 10 or later or Windows Server 2016 or later then they should get an update to Fx 128.3.0esr on or after Oct 1st. Windows 7, 8, 8.1 users should not get an update and if so then it was a mistake.

An update of some good news. Firefox 115 ESR may be getting more updates support till as late as March 2025 with 115.21.0esr. They will be making a decision in early 2025 on EOL date.