That icon has been removed, and the functionality provided in panes.  When other 
icons are added, the code about them currently has to be copied between 
tabulator.js for the online version and test.js for the extnsion version.  Any 
reason why it should't be in a common file?

Some icons (most notably the "Open in new window" icon) are not properly
displayed in the extension.  In the case of the "Open in new window" icon, it is
because of the following code:

                var linkButton = myDocument.createElement('input');
                linkButton.type='image';
                linkButton.src='icons/document.png';
                linkButton.alt='Open in new window';
                /*linkButton.onclick= function () {
                    return window.open(''+obj.uri,
				       ''+obj.uri,  'width=500,height=500,resizable=1,scrollbars=1')
                }*///TODO: Reimplement this.
                linkButton.title='View in a new window';
                rep.appendChild(linkButton);
        }

at outline.js#1490 , which indicates that the button doesn't even work
currently, anyway.  Icons need to be loaded into the Icon array the same way as
the other ones are in order to maintain consistency and guarantee functionality
in both the extension and the web app.

Other icons that this applies to include but may not be limited to the compass
rose / clock icons that indicate mappable / calendar-able data.