How to use Drosera ???

I'd like to use Drosera (WebKit JavaScript debugger) within this page :

<http://www.yvon-thoraval.com/JS/location.xhtml>

i know how to attach Drosera to WebKit or to the latest build but not
how to play with it.

basically, i want to understand why such a simple instruction as :

for(var i in document.location)
alert(<properties of document.location>)


isn't working under WebKit but is under Firefox 2, GranParadiso alpha2,
Opera 9?2

???

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