Anyone who spends a lot of time writing / editing HTML and CSS should spend some time to learn how to use browser development tools. All the features shown here are easily accomplished using built-in tools. And a lot more
Is there a way to do that in Firefox Developer Tools? If so, I would like to know because I would use it.
You could start with something like this - https://www.youtube.com/watch?v=S36N8RGdY2U
Chrome has "Copy Styles", but that doesn't get breakpoints. I don't know if Firefox does, but I haven't looked very much. It doesn't look like Safari does either.