Version 3.1 of my Safari content blocker StopTheFonts is available now in the App Store. This update fixes a bug with iCloud sync (introduced in version 3.0) where an iCloud error alert could be shown twice.
I also wanted to mention that I added a little tutorial to the StopTheFonts online support documentation, explaining how to use the Safari web inspector to see the web fonts blocked by StopTheFonts. As always, please contact support (me) with your questions!