Once I had gotten Fiddler to run (had to tell Mono to run in 32 bit mode) and I had re-created the settings.txt file, I received this error when trying to capture traffic:
Fiddler/FiddlerAttach.applescript:7:87: execution error: /bin/sh: USB,127.0.0.1,8888,on,127.0.0.1,8888,on,0,0,off,0,0,off: command not found (127)