What's the point of categorizing #bookmarks into folders if it's so slow, cumbersome, and angering to scroll though many #folders when trying to find one to add a bookmark to?
It could be a "fast search" line, like in the Ctrl+f feature - visible as a line under (or above) the folder tree, just after expanding the "Location" box.
So it could use the existing fast search engine - it would be easier to implement.
Why this hasn't been done yet is confounding! This is such a basic, necessary function, it's as if the designers don't actually do any bookmarking themselves.