http://h34nug3iwqjf2376fmmzdhgqivckzemcujmarlptfqeqtq7vya47yyad.onion/2008/04/20/sitebar-centralized-bookmarking/index.html
That’s why the sitebar-menu will show up when right clicking the bookmarks under Firefox, but in Opera you will need to use CTRL left-click to get the same menu. As for use in Opera, I prefer getting Opera’s menu when right-clicking, which means you can open bookmarks in new tabs and such. Adding bookmarks is simple too.