If The Kindle Previewer Won't Start 📎
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. export JAVA_HOME="/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home"