I am looking and I don't see my preferred extensions without which I cannot live (I won't repeat the already mentioned ones):

- Selection Context Search - very extensible addon which will allows you to select in page and use that for opening an URL: search in any engine, add to search strings in Wikipedia, IMDB, torrents, almost anything

- Ant Video Downloader - downloads any video from page

- Bookmark Tab Here - bookmark by right clicking directly on bookmark folder

- HistoryBlock - blocklists sites from history (for example google.com, your search history)