I had to look it up, but I guess this is what you are referring to:
https://support.mozilla.org/en-US/kb/categorizing-bookmarks-...
Yeah. It’s really easy to use set and intuitive to use. The only caveat is you still need to bookmark the site. But that makes a lot of sense when you think about it (how else are you going to catalogue the sites?).
I used it multiple times a day as it’s ridiculously handy.