| Yet Another Remove It Permanently | | - | | |
| Yes popups | | - | | |
| XHTML Mobile Profile | | - | | |
| Word Highlighter | | - | | |
| White on Black | | - | | |
| White List Ninja | | - | | |
| Website Theme Manager (802681) | | - | | |
| Website Theme Manager | | - | | |
| WebMail Ad Blocker | | - | | |
| Web Page Fixer + | | - | | |
| Web Marker | | - | | |
| Web Highlighter by Diigo | | - | | |
| Wallflower | | - | | |
| Vocabulary Highlighter | | - | | |
| Visited Link Supporter | | - | | |
| Visited | | - | | |
| Violentmonkey | | - | | |
| ViewPageAsImageAndSaveMemory! | | - | | |
| View as text | | - | | |
| User Style Manager | | - | | |
| Updated Ad Blocker for Firefox 11+ | | - | | |
| Unlinker | | - | | |
| URLFilter | | - | | |
| URL Tooltip e10s | | - | | |
| URL Tooltip WE | | - | | |
| URL Tooltip | | - | | |
| Twitter Disconnect | | - | | |
| Turn Off the Lights Mini | | - | | |
| Turn Off the Lights | | - | | |
| Tranquility | | - | | |
| Toggle Word Wrap | | - | | |
| Toggle Document Colors | | - | | |
| TitleQ | | - | | |
| Tile Tabs | | - | | |
| The Night Owl | | - | | |
| Textmarker | | - | | |
| TextForma SE | | - | | |
| TextForma | | - | | |
| TextBlockZoom | | - | | |
| Text Rewriter | | - | | |
| Text Highlighter | | - | | |
| Tampermonkey | | - | | |
| Tagu | | - | | |
| Tablenator | | - | | |
| TableTools2 | | - | | |
| TabColor | | - | | |
| Tab Slideshow | | - | | |
| Tab Permissions | | - | | |
| Tab Auto Reload | | - | | |
| Tab Auto Refresh | | - | | |