[1.8] Avoid exception in the case of <unknown> url eg https://bugzilla.mozilla.org/show_bug.cgi?id=646090
[1.8] Avoid exception in the case of <unknown> url eg https://bugzilla.mozilla.org/show_bug.cgi?id=646090

http://code.google.com/p/fbug/source/detail?r=9873

firebug/tracing-console,firebug/tracing-console