According to wikipedia, kmz is a:
DescriptionKeyhole Markup Language is an XML notation for expressing annotations and geographic visualizations within two-dimensional maps and Internet-based land-based browsers. KML was developed for use with Google Earth, which originally called Keyhole Earth Viewer.
However, the KMZ file exported by Google Earth is not an XML file. This is not even an XML file but a binary file.
How to see the XML content?