Hi cherchio,
Did you update directly from 2.3.2 to 2.5M3? Notice that a new Web Simulator was introduced in 2.5M1, where the debugging proccess is different than it is on Test Center.
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 our docs 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/