Sorry about this but, as Nightowl says, your configuration is 6 years out of date. Misago uses stuff that wasn't around then. Have you tried using a more modern browser with Vista to see if that works?
I think it's unreasonable to expect website developers to continue supporting OS's that are no longer supported by their manufacturers or browsers that are too far out of date. I think Mozilla ceased support for FF v52 in 2018.
They may work now, but without (at least) an up-to-date web browser, you'll find it increasingly difficult to use modern websites. The evolution of things like CSS standards continues, browsers add support for the new features, developers start using them, and it becomes too much work to apply workarounds for older browsers.
You'll find they also have a minimum OS requirement. Firefox currently requires Windows 7 or newer (I imagine that will change soon), and Chrome released their final version for Windows 7 and 8/8.1 in January - making Windows 10 their new minimum.
Yes , I've tried , but Firefox 52 is the latest update compatible with Vista.
Unfortunately , if I want to be active at this website , I have to finally say 'bye-bye' to my 14 years old computer...
I did not try , because mostly , I did not have problems when using this configuration.
Anyway , I just have started to use a computer with Windows 10 and Firefox 111.0.1 .