Tom,
You can use the Mobile Web Simulator for initial debugging of your app.
See this guide for working with the Simulator: http://docs.myeclipseide.com/index.jsp?topic=%2Fcom.genuitec.eclipse.mobile.doc%2Fhtml%2Ftutorials%2Fmobile_simulator%2Findex.html&cp=1_6_1_3
From the Simulator’s device panel, right click and choose “Inspect Element”. This will open the Chrome Developer Tools on the html5 app enabling you to inspect, set breakpoints and edit html (DOM), css styles and inline javascript and javascript files.
A key reason for the Simulator running on the Chrome browser is to enable developers to use the awesome Chrome Developer Tools. We are updating the doc above with additional info about the Chrome Dev Tools. In the meantime here is a great starting point:
Chrome Dev Tool docs: https://developers.google.com/chrome-developer-tools/
Chrome Dev Tool videos: https://developers.google.com/chrome-developer-tools/docs/videos
If you have already tried this on Mac and still cannot debug, please share the screenshot of the issue along with the steps you are following to debug.
Also share the .log file contents which is located at <workspace dir>/.metadata/.log to help us investigate further.