edit: I've now changed my mind on all this and don't use source-map debugging at all. First, it was generally flaky. Second, if I'm not writing JS I should at least be able to read it so I always debug in js.
First, keep in mind that source map debugging is flaky in Chrome right now. A couple things you can try:
Put a debugger statement in your code. I've noticed that the debug is very flaky -- about 10% of the time it just won't stop on breakpoints.
Open the coffee file directly by pressing Ctrl O in the sources pane then place breakpoints or use debugger statements.
Figure out why
"sourceRoot": "",
is empty. It's possible that that just means that the source file will be in the same directory as the js file (seems likely). My coffee files are in a different directory so they have a sourceRoot entry.Generate the source maps with grunt or coffeescript. This seems unlikely to have an effect though.
I'm betting #2 will do it.