In recent nightly builds (I've noticed this in the past week, though I can't say I tested it before then), running in Tiger (10.4.7 and 10.4.8, also only tested on PPC), clicking a link to a URL for a protocol that doesn't have a helper app registered on that particular system causes the Finder to come to the foreground with a window showing the contents of the Resources folder in /Applications/Safari.app, even though the app that's passing the URL is /Applications/WebKit.app, regardless of if WebKit or Safari is set as the default browser on the system. For example, exp2://234087932485 or h2tp://2309849, or any other nonsense URL for an unregistered protocol will triger this.
*** This bug has been marked as a duplicate of 11146 ***