I did try installing manually, both the new version and my last working version. I also tried just copying the file directly into the Library folder where calibre plugins live. It copied, but did not activate.
I have a feeling it is the Mavericks update to OSX behaving badly about permissions to install things. Even though I'm signed in as an admin, Mac has always asked for the password again before installing things. It seems like mavericks is taking permissions to a stricter level, however usually it will offer the username/password if it needs permissions during an install. Now I'm kicking myself because I removed the old version and now I'm without anything.
If you want me to test anything on my macs, I would be happy to help. Your plugin is great and I'd love to contribute.
Do you know of any other tools ffnet hasn't shut down yet?