This website says certain features work on firefox. But they don't. You can disregard firefox if you like. But if this "Modern CSS Code Snippets" website explicitly tells me their snippets work in firefox, I expect the snippets to work in firefox. Many of them do not.

again, "widely available" should not be intended in the general sense but as a much more precise industry term. "Baseline widely available" is defined[1] as a feature which has been available on all the core browsers (Chrome desktop and Android, Edge, Firefox desktop and Android, Safari on Mac and iOS) for two and a half years

[1]: https://web.dev/baseline

I don't really care about someones phony definition of widely available. If it runs on 90% of user's browsers, it's widely available. I'll gladly make a web page that puts this definition online so that you can also reference it in discussions, if you want.