| Copy ShortURL | | - | | |
| Copy Tiny URL | | - | | |
| Copy goo.gl URL | | - | | |
| Copyright Infringement Finder | | - | | |
| Craigslist Fusion | | - | | |
| Craigslist Peek | | - | | |
| Currency Converter | | - | | |
| DA Ghost | | - | | |
| Daily Dilbert | | - | | |
| Danbooru Downloader | | - | | |
| Dark YouTube Theme | | - | | |
| Datum Find Image Copies | | - | | |
| Define Word | | - | | |
| Delicious Bookmarks | | - | | |
| Deng Google Bookmarks | | - | | |
| Dictionary Tooltip | | - | | |
| DictionarySearch | | - | | |
| Diigo Toolbar for Firefox | | - | | |
| Disconnect Search | | - | | |
| Docs Online Viewer | | - | | |
| Domain Details | | - | | |
| Domain Whois for FirefoxTM | | - | | |
| Download YouTube Videos in HD and MP4 | | - | | |
| Dr.Web anti-virus link checker | | - | | |
| Dr.Web scan link | | - | | |
| Dribbble New Tab | | - | | |
| Dualsub | | - | | |
| DuckDuckBang | | - | | |
| DuckDuckComplete! | | - | | |
| DuckDuckGo Plus | | - | | |
| DuckDuckGo-bangs | | - | | |
| East Asian Translator | | - | | |
| Easy JsBin | | - | | |
| Easy YouTube Theme Maker | | - | | |
| Echofon | | - | | |
| Eiga.com Check-in Alert Notifier | | - | | |
| Email This! Bookmarklet Extension | | - | | |
| Email Yourself! | | - | | |
| Enjoy Browser | | - | | |
| Evernote Web Clipper | | - | | |
| Exch | | - | | |
| Exposure New Tab | | - | | |
| F1 by Mozilla Labs | | - | | |
| Fast Image Research | | - | | |
| Fast Image Search | | - | | |
| Fast Search by Surf Canyon | | - | | |
| Fast Translate | | - | | |
| Fast Translation | | - | | |
| FastBrowz | | - | | |
| FastestFox | | - | | |
