Hi, which update? Are you looking to update Firefox -- that's free, or Windows -- ask Microsoft, or something else?

Your UserAgent or UA appears to be Mozilla/5.0 (Windows NT 6.2; Win64; x64; rv:109.0) Gecko/20100101 Firefox/115.0

It appears you are using Firefox 115 on Windows 8.1 ?

Firefox 115 ESR is the last to still support the eol Windows, 7, 8, 8.1 as Firefox 116.0 and later requires Windows 10, 11 to run for Windows version. The Firefox 115 ESR will be updated 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

Mozilla does not charge for Firefox installs or updates for any Firefox web browser on Windows, macOS, Linux or mobile versions for iOS/iPadOS and Android.