The location of XPCOM components can be specified by a global variable $XPCOM_PATH. Set the path to the component directory to this variable before executing requiring 'xpcom' first time. Environment variable MOZILLA_FIVE_HOME can be used to overwrite this setting.
If neither variable is defined, the rbXPCOM fall back to a default directory which is depend on the platform. On UNIX, the default is current directory. On Windows, it is the directory from which xpcom.dll.