Perhaps you use Firefox on Windows.
Firefox on Linux has much more problems than Firefox on Windows, mostly because it does not support many GPUs, so it frequently disables WebGL or it cannot use hardware support for playing videos, even now, in 2026. This breaks many sites.
Unlike Firefox, the Linux versions of Vivaldi/Chromium/Chrome do not appear to have any deficiencies in comparison with their Windows versions.
Which is not Firefox's fault. It's up to the operating system to provide a stable API to make things like this work.
That has not been my experience of Firefox on Linux.
Whenever I encounter a broken site, it's because I blocked some advertising scripts and the whole thing fell apart with a slew of JavaScript errors. I'm quite happy to avoid such shoddy sites.