Your question is not specific. If you want to remove Mozilla from your computer simply uninstall it from Add/Remove button from Control Panel of your computer.
How Can I Cancel Mozilla Firefox?
You mean uninstall Firefox browser? Start, Control Panel, Add Remove.
Want to uninstall Mozilla Firefox? Click Start>Control Panel>Add/Remove Programs>Choose Mozilla Firefox>click Remove. Or you can use a professional removal to deal with it.
Did you mean Uninstall?
Uninstall it! =P Start/control panel/programs/Uninstall a program/find it/delete it! Simple as that! :)