It is very difficult to change the URL under Properties View for an object.
If I click (once) on the URL text field, an "Open" File dialog opens which is not useful when I want to enter text (http://...).
I've found that I can enter the text htrough the Structure View->Properties->Data, but that is a long path just to enter a URL.
I've experience this on MacOSX 10.6.8.