| SlyZoom | | - | | |
| SmallWinFit | | - | | |
| Smart Zoom | | - | | |
| Smooth East Asian Fonts | | - | | |
| Snow | | - | | |
| Split Browser | | - | | |
| Split Pannel | | - | | |
| Statusbar Charset | | - | | |
| Stop All Ads | | - | | |
| Stop SNS | | - | | |
| Stop-it | | - | | |
| StyleRRR - Barebones Userstyle Injector | | - | | |
| Styler | | - | | |
| Styles Tuner | | - | | |
| Stylish | | - | | |
| Stylus | | - | | |
| SusBlocker | | - | | |
| Tab Auto Refresh | | - | | |
| Tab Auto Reload | | - | | |
| Tab Permissions | | - | | |
| Tab Slideshow | | - | | |
| TabColor | | - | | |
| TableTools2 | | - | | |
| Tablenator | | - | | |
| Tagu | | - | | |
| Tampermonkey | | - | | |
| Text Highlighter | | - | | |
| Text Rewriter | | - | | |
| TextBlockZoom | | - | | |
| TextForma | | - | | |
| TextForma SE | | - | | |
| Textmarker | | - | | |
| The Night Owl | | - | | |
| Tile Tabs | | - | | |
| TitleQ | | - | | |
| Toggle Document Colors | | - | | |
| Toggle Word Wrap | | - | | |
| Tranquility | | - | | |
| Turn Off the Lights | | - | | |
| Turn Off the Lights Mini | | - | | |
| Twitter Disconnect | | - | | |
| URL Tooltip | | - | | |
| URL Tooltip WE | | - | | |
| URL Tooltip e10s | | - | | |
| URLFilter | | - | | |
| Unlinker | | - | | |
| Updated Ad Blocker for Firefox 11+ | | - | | |
| User Style Manager | | - | | |
| View as text | | - | | |
| ViewPageAsImageAndSaveMemory! | | - | | |
