| Inactive tab | | - | | |
| Indexify Tabs | | - | | |
| Informational Tab | | - | | |
| Inquiry Bar | | - | | |
| Insert Tab on Right | | - | | |
| InstantFox Quick Search | | - | | |
| IrisFox | | - | | |
| Keyword Search | | - | | |
| Keyword Search (WebExtension) | | - | | |
| KinGumo | | - | | |
| Konquefox | | - | | |
| LCD Clock | | - | | |
| Language Button | | - | | |
| Last Selected Tab | | - | | |
| Last Tab | | - | | |
| Last Tab Close Button | | - | | |
| LastTab | | - | | |
| Layout Plan | | - | | |
| LeftSideStar | | - | | |
| LessChrome Modified | | - | | |
| LesserChrome | | - | | |
| Lighterweight Themes for Australis | | - | | |
| Limit Tabs | | - | | |
| Link Location Bar | | - | | |
| LinkParser | | - | | |
| List All Tabs Menu | | - | | |
| List Tabs | | - | | |
| Load Control | | - | | |
| Load Progress Bar | | - | | |
| Load Tab on select | | - | | |
| Load Tabs Progressively | | - | | |
| Load Tabs Progressively Fixed | | - | | |
| Load on Select | | - | | |
| LoadTabOnSelect | | - | | |
| Loading Bar | | - | | |
| Location Alerter | | - | | |
| Location Bar Characters | | - | | |
| Location Bar Enhancer | | - | | |
| LocationBar2 (modified) | | - | | |
| Locationbar Limit | | - | | |
| Locationbar2 | | - | | |
| Locationbar3 | | - | | |
| Long Click | | - | | |
| Luddite UI | | - | | |
| MClickFocusTab | | - | | |
| ML Progress Bar | | - | | |
| MMB address to reload | | - | | |
| MRU Tabs | | - | | |
| Magic Tab | | - | | |
| Make Address Bar Font Size Bigger | | - | | |
