I think it's mostly a very good idea, but much less accessible compared to the omnipresent bookmarks bar, so I will keep using the bookmarks bar (whose primary downside is the vendor lock in, imo).
My point is: the file explorer seems to have (at least for me) a far better UX than the browser's bookmark bar.
Example: you accidentally renamed a bookmark in the bookmark bar. Can you do CTRL-Z? No! With files in file explorer, you could.
Also im a avid user of keyword bookmarks in Firefox, so I need to store those in Firefox anyway for them to work
I fail to see how bookmarks have vendor lock in. Every browser I've used has bookmark import/export to a format understandable by other browsers, like HTML.