Which version am I running on my Windows 7 computer?

115 ESR is fine and appropriate for Win7, however you may just need to uncheck "run in compatibility mode" on the windows shortcut, as it for some reason thinks it's being run under Vista.

Hello

What is the latest browser?

Firefox support for Windows 7, 8 and 8.1 https://support.mozilla.org/en-US/kb/firefox-users-windows-7-8-and-81-moving-extended-support

https://connect.mozilla.org/t5/discussions/help-gt-about-firefox-gt-update-to-115-17-0esr-on-windows-7/m-p/133880/highlight/true#M53822

The older Firefox 115 ESR (based on the old Firefox 115 Release) is still being updated with security/stability fixes for the EOL Windows 7, 8, 8.1 and macOS 10.12, 10.13, 10.14 OS users so they can still have a secure web browser for a time. Mozilla extended update plans to keep Fx 115 ESR updates going till March 2027.

Otherwise you need Windows 10 or 11 or to use Linux to be able to use current versions from Fx 116.0 and later like Firefox 153 Release and Firefox 153 ESR.