Hi, Microsoft Windows Server 2012 R2 is equivalent to Win8, so Firefox ESR 115.* is supported.

Ok Thank you, do you know where I can download this version safely (so from Mozilla resources) ?

https://www.mozilla.org/firefox/windows/ This page doesn't recognize your environment? It should, as far as we know.

I'm trying to download it from my Windows 11 machine - I don't have access to Windows Server 2012 - I just want to download the version Mozilla Firefox ESR 115.16.1 (x64 en-US) in order to create a package and send it to vulnerable servers since October this version is no longer present in application catalogue for PMP (https://patchmypc.com/firefox-esr-not-in-app-catalog)

Try https://ftp.mozilla.org/pub/firefox/releases/115.16.1esr/win64/

Perhaps someone will give you a better URL later.

The link is perfect, thanks a lot for you help!

Mozilla has said they prefer one uses https://archive.mozilla.org over https://ftp.mozilla.org as I guess this was from when the ftp:// protocol was in use before up till August 5th, 2015.

https://archive.mozilla.org/pub/firefox/releases/115.16.1esr/

Mozilla used to serve the older Firefox 115 ESR along with Firefox 128 ESR on https://www.mozilla.org/firefox/all/ https://www.mozilla.org/firefox/all/desktop-esr/ but stopped when they thought Fx 115.15.0esr was going to be the last planned update. Then a bit later they decided they would continue updates until at least Fx 115.21.0esr in March 2025. https://whattrainisitnow.com/release/?version=esr

Also keep in mind that the Firefox 115 ESR updates is in support of the eol Windows 7, 8, 8.1 and macOS 10.12, 10.13, 10.14 users in mind so those using Firefox 115 ESR on Windows 10/11 or macOS 10.15+ will get update prompts to Fx 128.x.0 ESR.

edit: Also for Windows Server OS, the oldest Windows server you can run Firefox 116.0 and later on is Windows Server 2016 since it is based on Windows 10.