I would like to stress that you did not “restore full functionality” to the forum.
Discourse performs a browser capabilities check (here) for things it relies on, and sets the unsupportedBrowser flag accordingly. Your browser fails those checks.
Overriding that flag does not restore features in the browser that were never there, it will make Discourse fail in various places.
If the developer team was to actually make Discourse work on FF 115 ESR they would have to build polyfills for features like for example CSS :has , light-dark() , relative colors and some more. Those features are used by Discourse and not supported by Firefox ESR 115. The amount of time/lines of code spent on your flag override are nowhere near the effort that is required to actually make things work by building those polyfills. Those are the developer resources I am talking about.
We can debate whether a hard block is better than having fail something (semi-)gracefully but that is their call to make and not ours.