Yes, you can use Firefox 115 ESR. Mozilla is providing security updates through the Firefox ESR channel up until the end of ESR version 115, at least to September 2025.

Firefox 116.0 and later requires Windows 10, 11 (and macOS 10.15 or later) to run.

As said there is the Firefox 115 ESR still being supported with updates as Fx 115.21.0esr was recently released on March 4 and the updates will continue till Fx 115.27.0esr in August unless Mozilla extends updates a third time. These are being provided with Window 7, 8, 8.1 and macOS 10.12, 10.13, 10.14 OS users in mind.

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

/moved thread from Firefox for Android to Firefox section.