type “File:///”. The capital ‘F’ is important. On the third /, it crashes.
And the crash reporter, Mail, and even the Spotlight menu can crash when displaying the text. In some apps you can prevent the crash by unchecking Edit ‣ Substitutions ‣ Data Detectors. For Mail, there’s a defaults command.
Update (2013-03-16): The bug appears to be fixed in Mac OS X 10.8.3.
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