Prior to Firefox 62 you were able to add notes/annotations to a Bookmark and Bookmark Folder.
I heavily used this feature to:
- Further describe the contents and purpose of Bookmarks in the Bookmark Folder.
- Add additional usage information to the JavaScript Bookmarks that were listed on my Bookmarks Toolbar.
When I found the Firefox Bookmark Notes Extension created by Jase in the Firefox Add-Ons I installed it on my test system (a cut-down copy of my existing system running within a VM). Sadly it had too many issues and I soon removed it. Also it looks as if nothing will change in it as the last version was released in 2018 which was before Firefox started using WebExtensions.