Hello, Better Bookmark author here. This extension is not meant to open anything - it's only purpose is simplifying the process of adding new bookmarks. It basically displays a list of your bookmark folders (flattened), and lets you select which folder the bookmark should go to. If you click on a folder (or navigate using arrows and confirm with enter), it should close the menu, but the page should be bookmarked into this folder. If it doesn't do it, it's a bug :)