| Remote XUL Manager | | - | | |
| Regxer | | - | | |
| Rainbow | | - | | |
| PopupInspector | | - | | |
| PixelZoomer | | - | | |
| Pixel Perfect | | - | | |
| PixeRoll | | - | | |
| Phoenix | | - | | |
| Performance-Analyser | | - | | |
| Performance Map | | - | | |
| Palette Creator | | - | | |
| PageDiff | | - | | |
| Page Speed | | - | | |
| PHPdebugger | | - | | |
| Originz | | - | | |
| OpenWAX | | - | | |
| Open TortoiseSVN | | - | | |
| My Scratchpad | | - | | |
| More Display Resolutions | | - | | |
| MobileView | | - | | |
| MiniBrowserX | | - | | |
| MileWideBack | | - | | |
| Meta Generator Version Check | | - | | |
| MeasureIt | | - | | |
| Measure-it | | - | | |
| Magnifier | | - | | |
| Local Load | | - | | |
| Live editor for CSS and LESS - Magic CSS | | - | | |
| Live Editor | | - | | |
| Live Edit | | - | | |
| Library Detector | | - | | |
| Landmark Navigation via Keyboard or Pop-up | | - | | |
| L-Square | | - | | |
| Javascript View | | - | | |
| Javascript Command | | - | | |
| JavaScript Terminal | | - | | |
| JavaScript Deobfuscator | | - | | |
| JSView | | - | | |
| JSONView | | - | | |
| JSON-DataView | | - | | |
| JSLinter | | - | | |
| JS Deminifier | | - | | |
| InspectThis | | - | | |
| Inspect Object | | - | | |
| Input Colourer | | - | | |
| Inline Code Finder for Firebug | | - | | |
| Inline Code Finder | | - | | |
| IndexedDB Browser | | - | | |
| ImageExchange | | - | | |
| Image Spider | | - | | |