| Manage My Tabs - Tab Manager | | - | | |
| Max Loaded Tabs | | - | | |
| Max Tab Toggle | | - | | |
| Max Tabs | | - | | |
| Maximize／Restore Window Button | | - | | |
| MediaPimp | | - | | |
| MemChaser | | - | | |
| Menu Button Reskin | | - | | |
| Menu Editor | | - | | |
| Menu Editor II | | - | | |
| Menu Mod | | - | | |
| Menu On Top | | - | | |
| Menu Ontologist | | - | | |
| Menu Wizard | | - | | |
| Metal Lion Addressbar Improvements | | - | | |
| Middle Click On Page Closes Tab | | - | | |
| Middle Click Tabbar | | - | | |
| Middle Click on Tabbar to Undo Close Tab | | - | | |
| MinUI | | - | | |
| Mind the Time | | - | | |
| Mini Tab | | - | | |
| Minimal Digital Clock | | - | | |
| Minimalist Bookmarks Toolbar | | - | | |
| Minimalist UI | | - | | |
| Minimize Window Button | | - | | |
| Minimode | | - | | |
| ModestTab | | - | | |
| More Bookmarks Toolbar | | - | | |
| More Tools Menu | | - | | |
| More or Less Browser Window Padding | | - | | |
| Most Recent Tab | | - | | |
| Mouse Dictionary | | - | | |
| Movable Firefox Button | | - | | |
| MovableReload29 | | - | | |
| Move Active Tab To Left | | - | | |
| Move To Window | | - | | |
| MoveTab | | - | | |
| Mozilla Labs： Prospector - AwesomeBar HD | | - | | |
| Mozilla Labs： Prospector - Find Suggest | | - | | |
| Mozilla Labs： Prospector - Instant Preview | | - | | |
| Mozilla Labs： Prospector - LessChrome HD | | - | | |
| Mozilla Labs： Prospector - OneLiner | | - | | |
| Mozilla Labs： Prospector - Speak Words | | - | | |
| Mozilla Labs： Prospector - Tab Focus | | - | | |
| Multi Easy Search | | - | | |
| Multi homepage | | - | | |
| Multi-Tab Close | | - | | |
| MultiSelect Tabs | | - | | |
| Multifox Toolbar Button | | - | | |
| Multiple Tab Handler | | - | | |
