BrowserLab just gives you screenshots. You can't actually interact with a site like you can with say Adobe Device Central in Creative Suites which otherwise do nearly the same thing.
If you require interaction, you should look into another solution like a virtual machine or emulator.
Scott is somewhat correct. BrowserLab currently does only return screenshots and does not allow for live interactive testing on our servers. However, if you test using Firefox, you can make use of our BrowserLab for Firebug add-on to interact with your web page locally, and request screenshots of the local content from our servers.
You can find more details on the solution here: http://blogs.adobe.com/browserlab/2011/08/22/testing-private-content-with-browserlab/
Hope this helps,