https://caniuse.com/?compare=firefox+120,and_ff+119&compareCats=all

If you scroll down past the browser version checkboxes (I’ve ticked the right ones for you) and list of features FireFox supports, you’ll find a very long list of web features that don’t work (or don’t work properly) in FireFox.

Some of them are pretty important features and there are sites that use them. Pretty sure Google Sheets uses the Filesystem stuff for example - it “works” in FireFox but not as well as in Chrome.

What this article is about is unless FireFox’s marketshare trend reverses, websites are going to stop including workarounds specifically for FireFox users. They’ll just let the site be broken in that browser.

I always get annoyed by the copy paste thing. I can’t remember which way it goes but you either can’t copy paste with the mouse or with Ctrl c/v. That’s the only thing that bugs me about FF and sheets.