| Outlook 2003 Silver | | - | |
| Outlook 2003 Green | | - | |
| Outlook 2003 Blue | | - | |
| Orthodox for Firefox | | - | |
| Orbit Yellow 2006 | | - | |
| Orbit Orange | | - | |
| Orbit Grey Custom | | - | |
| Orbit Grey | | - | |
| Orbit Blue | | - | |
| OrangeShift | | - | |
| OpenWorld_Win | | - | |
| OpenWorld | | - | |
| Onyx | | - | |
| OldFactory Black | | - | |
| OldFactory | | - | |
| Office Black | | - | |
| N－Scape1 | | - | |
| Nuvola FF | | - | |
| Nuri | | - | |
| Noia Fox | | - | |
| Noia 4 | | - | |
| Noia 2.0 (lite) | | - | |
| Noia 2.0 (eXtreme) | | - | |
| Netscape Windows 3.1 | | - | |
| Netscape Navigator Nostalgia | | - | |
| Nautipolis | | - | |
| Nautical Classic | | - | |
| Native XP | | - | |
| NEWA | | - | |
| NASA Normal | | - | |
| NASA Night Launch(724448) | | - | |
| NASA Night Launch | [Fx_MinVer] | - | [Fx_MaxVer] |
| N2Scape | | - | |
| Myzking | | - | |
| Mozilla.org | | - | |
| Moxxi | | - | |
| Mostly Crystal | | - | |
| Mosaic-Fox | | - | |
| Mongrel | | - | |
| Modern Toolbar Icons | | - | |
| Modern Pinball | | - | |
| Modern Modoki | | - | |
| Modern Aluminum | | - | |
| MidnightFox | | - | |
| Microfirefox | | - | |
| MicroFox | | - | |
| Metal for Firefox | | - | |
| Metal Lion － iCe | | - | |
| Metal Lion － Brushed iCe | | - | |
| Metal Lion Australis Tiger SP | | - | |