Not sure why it's so hard to provided newer versions to win 7.
Well if you want to keep using Win7 (and RADIUS with MD5 while you are at it) go ahead, no onee is stoping you, there are firefox derivatives that still support Win7, one of the advantages of FOSS
Also, remember that, between FF115 and FF128 a year of development has lapsed, who knows if anything in the codebase changed that made the browser incompatible with Win7, is not "one more version" more like 13 "incrementals"
Some other people want to to keep their computing systems secure, starting with the foundation (the OS), and moving upwards (browsers, porotocols and APPs)
May I remind you that Win10 (and 11) introduced additional security protections and APIs not present on Win7... and may I remind you that Win7 not seen a security patch sionce Jan 30, 2023?
Right you get 1 version and nothing newer. And many sites now toss you if your not running newer versions.
I guess that getting support from Jan 2023 until Sept 2025 is better than nothing, and certainly much betyter than the support you got from the OS manufacturer's browser. And FWIW, I use FF ESR as my main browser, and, for the last 3 years, never encountered a site complaining about ESR beaing an old version. Yes, four or more years ago it was a big problem, but nowadays, not so much.