| Custom Buttons | | - | | |
| Custom New Tab | | - | | |
| Custom New Tab Button | | - | | |
| Custom New Tabs | | - | | |
| Custom Tab Width | | - | | |
| Custom Titlebar Text | | - | | |
| CustomAppButton | | - | | |
| Customize Palette Fix | | - | | |
| Cut，copy and paste Tabs | | - | | |
| CyberSearch | | - | | |
| DNSSniffer Toolbar | | - | | |
| Dblclick Reset Searchbar | | - | | |
| Delete Tab | | - | | |
| DevEdition theme enabler | | - | | |
| Disable Tabs | | - | | |
| Do Not Auto Activate Pin Tabs | | - | | |
| Domain in Title | | - | | |
| DomainActions | | - | | |
| Dormancy | | - | | |
| Double Click Add New Tab | | - | | |
| Double Click New Tab | | - | | |
| Double Click Tab Pinning | | - | | |
| Double Click Top-Left to Close | | - | | |
| Double-click To Reload Tab | | - | | |
| Draggable Star | | - | | |
| Duplicate 2 Window | | - | | |
| Duplicate Tab | | - | | |
| Duplicate Tab Blocker | | - | | |
| Duplicate Tab Closer | | - | | |
| Duplicate Tab Hotkey | | - | | |
| Duplicate Tab Hotkey fork | | - | | |
| Duplicate Tab Shortcut | | - | | |
| Duplicate Tabs Closer | | - | | |
| Duplicate This Tab | | - | | |
| Duplicate in Tab Context Menu | | - | | |
| Duplicate tab | | - | | |
| DuplicateX | | - | | |
| Duplicator | | - | | |
| Edit Tab Titles | | - | | |
| EditPrefs | | - | | |
| Email Link button | | - | | |
| Enter Selects | | - | | |
| Exit Button Firefox | | - | | |
| Export Tabs URLs | | - | | |
| Ez Sidebar | | - | | |
| FDock | | - | | |
| FF Fullscreen | | - | | |
| FF History | | - | | |
| FLST (Firefox 29+) | | - | | |
| FLST (Firefox 4+) | | - | | |
