Firefox 115 ESR is the last to support Windows 7, 8, 8.1 so Firefox 115.18.0esr should work on Windows 7. The Firefox 115 ESR will get updates till at least 115.21.0esr in March 2025 unless Mozilla decides in early 2025 to extend updates again. 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, 11

Not sure where you got Firefox 115.18.0esr from as https://archive.mozilla.org/pub/firefox/releases/115.18.0esr/win64/ and pick your language should work on Windows 7.

https://www.mozilla.org/firefox/115.18.0/system-requirements/ Operating Systems (32-bit and 64-bit) Windows 7 Windows 8 or 8.1

Looking at your UserAgent used to post this thread shows there is an issue. Mozilla/5.0 (Windows NT 6.0; Win64; x64; rv:102.0) Gecko/20100101 Firefox/102.0

The NT 6.0 is Windows Vista while Windows 7 is NT 6.1. Perhaps you are running Firefox 102 in Windows Vista compatibility mode on Windows 7 for some reason? as Firefox 52.9.0esr was the last to support Windows XP and Vista. This modified UA can explain the ""Unable to install this version requires Win 7 x64 or newer" message you got.

https://support.microsoft.com/en-us/topic/guided-help-software-designed-for-an-older-windows-os-cannot-run-on-windows-7-use-the-program-compatibility-mode-faf95048-3896-efe4-bd92-f173d5f89a07

115.18.0esr refuses to install. It responds "Sorry, Firefox can't be installed. This version of Firefox requires Windows 7 x64 or newer. Please click the OK button for further info."

Clicking the OK button takes me to a 133.0.3 page noted as Windows 10.

Note that I do not have 115.18.0 as you mentioned.

I am running 102.10.0esr (32bit because the 64bit version would not install) on Win7 x64. If it's relevant I'm running a 24 core Xeon CPU E5 2697 v2

Ok. Put Firefox into "Troubleshooting Mode" and restarted it. Then installed 115.18.0esr which appeared to be successful. (For the first time) But it wasn't. Computer froze and multiple attempts to kill Firefox in Task Manager failed. Each attempt resulted in 2 more entries for Firefox eventually 6 or 8. Everything locked up. Restarted (Hard) Laptop 3 times and each time I fired up Firefox same results in Task Manager and then everything froze. For unknown reasons the 4th attempt was successful. I hadn't changed anything. Now shows 115.18.0esr 64bit in about Firefox.

So "Successful" ? Only time will tell.

Again as I stated in my second reply it appears you are running Firefox 102 in Windows Vista compatibility mode. I posted a link on how to undo this. This modified Firefox UserAgent is why you are getting the message of "This version of Firefox requires Windows 7 x64 or newer if you are downloading from mozilla.org