Why does editing javascript in Chrome Developer Tools not work?

Chrome Webkit Inspector does not allow you to live-edit pretty printed Javascript. Click the pretty print button (Looks like { }) in the Scripts tab to disable pretty-print mode and edit it.

Source: Introduction To Chrome Developer Tools

You might have hit against the Same origin policy.

From Disabling cross-domain security check for AJAX development in Google Chrome :

Start Google Chrome from command line, Ubuntu/Linux:

chromium-browser --disable-web-security