| Mini Pixiv | | - | | |
| Mini Map Sidebar Extension | | - | | |
| Miiverse | | - | | |
| MementoFox | | - | | |
| Media URL Timestamper | | - | | |
| Media Player for YouTubeTM | | - | | |
| Media Converter | | - | | |
| Mark Ads Sites In Search | | - | | |
| Map ＆ More | | - | | |
| Map With Google | | - | | |
| Map This | | - | | |
| MSN for Firefox | | - | | |
| Lowest Price Checker | | - | | |
| Lovely forks | | - | | |
| Locator | | - | | |
| LiveDic | | - | | |
| Linkspy | | - | | |
| LinkExtend | | - | | |
| Lighter | | - | | |
| Light Dict | | - | | |
| Libron(リブロン) | | - | | |
| Let's Search | | - | | |
| Lens | | - | | |
| Latest BBC News | | - | | |
| LastPass | | - | | |
| Kloutify | | - | | |
| Klout | | - | | |
| KeyAffinity | | - | | |
| Keeper Password Manager ＆ Digital Vault | | - | | |
| KOSHIAN 連投抑制 | | - | | |
| KOSHIAN 返信フォーム拡張 | | - | | |
| KOSHIAN reload futaba | | - | | |
| KOSHIAN quote futaba | | - | | |
| KOSHIAN delフォームをポップアップで開く | | - | | |
| KOSHIAN autolink futaba | | - | | |
| KOSHIAN Show Mail | | - | | |
| KOSHIAN Popuper Quote | | - | | |
| KOSHIAN NG | | - | | |
| KOSHIAN Image Popuper | | - | | |
| KOSHIAN Float Form | | - | | |
| KOSHIAN Favicon Changer | | - | | |
| KOSHIAN Catalog Marker | | - | | |
| KJCLUB Basic Support | | - | | |
| KDDI ChatWork チャットワーク シングルサインオン | | - | | |
| Jingoo | | - | | |
| Jigsaw Puzzle Maker | | - | | |
| Japan-newspapers | | - | | |
| Janus | | - | | |
| JaffaSites | | - | | |
| J-WAVE ツールバー | | - | | |