I've been unable to create a zimlet where double clicking on the panel item opens a url in a new window. Double clicking it pops open a box labeled 'Test URL Preferences' with an ok button. What am I doing wrong?

<zimlet name="com_zimbra_url" version="1.1" description="Test URL">
<zimletPanelItem label="Test URL">
<toolTipText>This is a test zimlet</toolTipText>
<canvas type="window"/>
<actionUrl method="get" target="http://www.yahoo.com" />