Please note that after latest update of Google Chrome, WebGL has been accidentally broken. You may find 3DTin not working. We will keep monitoring the fix in Chrome WebGL, until then you can use Firefox to access 3DTin.
Update1: The problem seems only limited to Google Chrome on Mac OSX
Update2: A temporary fix is to launch Chrome from command line with this command:
open -a "Google Chrome.app" --args --disable-gl-multisampling
Update3: The bug was fixed in Google Chrome version 26.0.1410.65 for Mac OSX.