The Bookmarks Left pane (CTRL+B) tool in Firefox lacks mandatory features: searching in directory names, being able to get path of the parent directory of a bookmark, etc.
Addon “Bookmark search plus” does all that (and much more) and integrates particularly well with firefox.
IMHO it merits being looked into and advertised by mozilla.
Indeed, I struggled for years with the 2 features cited above, until I found deep into a forum discussion a mention of this addon. Please make so that people find it faster than I did! For instance by featuring it with a “recommended” badge on the addons.mozilla.org page!