It's baffling actually that Firefox doesn't let you annotate bookmarks, it seems such an obvious feature.
There was a financial conflict of interest, since Mozilla Corp was selling Pocket subscriptions where the ability to even just be able to have an unlimited number of highlights was a premium feature.
Firefox has an experimental Tab Notes feature now: <https://support.mozilla.org/en-US/kb/tab-notes-firefox>
(In the Firefox heyday, the bookmarks manager had a Description field that could be repurposed for adding notes.)
One of the things I started and didn't get back to with my hobbyist AI programming is a bookmark manager / URL cleaner. I should get back to thinking about the design for that. It's something I could actually use if I had it.