Kindle Previewer is a Java application, which seems to require JDK 1.6 and does not run on JDK 1.7.
To fix the environment, open
/Applications/Kindle Previewer.app/Contents/MacOS/Launcher and add JAVA_HOME pointing to your JDK 1.6 installation right after #!/bin/sh, e.g.
Classic Java EE 7 Workshops: Bootstrap, Effective and Architectures, July, 13th-15th
Online workshop: Java EE 7 Bootstrap