| Open Multiple Locations | | - | | |
| Open Link In Program (OLIP) | | - | | |
| Open As Webfolder | | - | | |
| OPIE2 | | - | | |
| OPIE | | - | | |
| O'Notes | | - | | |
| Numpad Typing Drills | | - | | |
| Notesaver! | | - | | |
| Notes | | - | | |
| Notebook-fox | | - | | |
| Note Taker | | - | | |
| Noia Fox options | | - | | |
| NoTea | | - | | |
| Night Launch Companion | | - | | |
| Nice-Calculator | | - | | |
| New Tab - Moment | | - | | |
| My Weekly Browsing Schedule | | - | | |
| My TimeZone | | - | | |
| My Notepad | | - | | |
| Mozilla Labs： Prospector - Query Stats | | - | | |
| Mouse Click Counter | | - | | |
| More About | | - | | |
| Moment | | - | | |
| Moji | | - | | |
| Mobile Barcoder | | - | | |
| MinimaList ― To-Do List | | - | | |
| Microsoft .NET Framework Assistant | | - | | |
| Menu Icons Plus | | - | | |
| Memory Fox | | - | | |
| Markdown Viewer | | - | | |
| Mar Mod Updated | | - | | |
| Mar Mod | | - | | |
| Lucifox | | - | | |
| Lookupper | | - | | |
| Local Filesystem Links | | - | | |
| Link Sgf Viewer | | - | | |
| Launchy | | - | | |
| LastPage | | - | | |
| Language Pack Install Helper | | - | | |
| LSD | | - | | |
| Kmoney | | - | | |
| Keyword Box | | - | | |
| Katakana 2 Romaji ／ カタカナからローマ字 | | - | | |
| JavaScript Actions Button | | - | | |
| JSA Menu K | | - | | |
| Internote | | - | | |
| Icon Effects | | - | | |
| Hourly Chime | | - | | |
| Hide in Plain Sight | | - | | |
| Hex Viewer | | - | | |
