Yes, Werner, you cannot install RC version directly by following the link anymore.
Google has recently forbidden to distribute the extensions directly from the web.
http://support.google.com/chrome_websto ... rx_warning
Follow these steps to install the extension for testing
1. Download the extension file from the website and save it to your computer.
2. Click the wrench icon on the browser toolbar.
3. Select Tools > Extensions.
4. Locate the extension file on your computer and drag the file onto the Extensions page.
5. Review the list of permissions in the dialog that appears. If you would like to proceed, click Install.