Bookmarks manager in side bar with simple interface and powerful features
-drag and drop single or multiple selected
-export bookmarks tree to HMTL file with favicons
-sort alphabetically, remove duplicates, merge folders
-search with folder structure
-open bookmarks with double click, middle click, single click, CTRL+click or drag out
-copy bookmarks url's to clipboard
-open bookmarks and folders by dragging them out of sidebar (if you don't like middle click or similar)
-save links by dragging them onto bookmarks tree or menu buttons (auto fetch title)
-save all tabs as bookmarks folder (session)
-bookmarks organized by Opera system into main folders
-right click menu, add new bookmark/folder, open in new window/incognito, cut/copy/paste...
... check gifs in "how to..." for visual explanation
*with "drag links on bookmarks tree" feature, extension needs to fetch link title trough XMLHttpRequest, and for that it needs "all_urls" permission in manifest.
This is presented to users as "This extension will access your data on all websites".