1. Firefox is the last browser that still supports Win7.
2. Websites can drop their support basing on the User Agent. You can install User Agent Switcher and set it to Firefox 136, Win10.

Chrome/Chromium based web browsers already dropped Windows 7, 8, 8.1 support back in Jan/Feb 2023.

Firefox 115 ESR still supports Windows 7, 8, 8.1 til Fx 115.27.0esr in August unless Mozilla extends updates again.

https://support.mozilla.org/en-US/kb/firefox-users-windows-7-8-and-81-moving-extended-support

The Firefox 115 ESR is based on the Firefox 115.0 Release so some current updated sites may work best in more current versions.

The only way to use more current versions of Firefox like 137.0.1 and 128.9.0esr is to use Windows 10, 11 or perhaps dual boot with a Linux distro though that may be a bit technical.

thanks for the suggestion. I looked at some of the issues users have with this extension and hesitant to use anything that could make things worse. However I really do appreciate the heads up on what to expect going forward.

Some web sites

You should contact with website owners. They could limit your right to use browser what you like. This discrimination exists.

My position is do not use webseites which spend my time without serious reason. Serious reasons do not exsists until 2009 year.

Some web sites have begun to not work with Firefox browser on Windows 7 64 bit.

Can you tell whether this is because you use Windows 7 or because you use Firefox 115? To fake your Firefox version number, there is a fairly simple option still available in Firefox 115:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren't fully supported.

(2) In the search box in the page, type or paste forceVersion and pause while the list is filtered

(3) Double-click the network.http.useragent.forceVersion preference to display an editing field, and change the value to 128 then press Enter or click the blue check mark button to save the change.

I don't remember whether that starts being relayed to sites immediately on the next request, or whether it takes effect after exiting out and restarting Firefox.