Before building the project the following must be done. 1. ..\..\..\bin\xpidl -m header -I..\..\..\idl nsIScriptablePlugin.idl This will generate nsIScriptablePlugin.h which is needed to successfuly compile the plugin 2. ..\..\..\bin\xpidl -m typelib -I..\..\..\idl nsIScriptablePlugin.idl This will create nsIScriptablePlugin.xpt file which should go to the Mozilla Components folder.