www.greenend.org.uk/rjk/tumblr on one browser, http://www.timeanddate.com/weather/germany/hamburg on the other for 'www' but https://apps.facebook.com/thesimssocial/ for 'www.' even though there's no 'www.' in that URL at all. (Firefox's all-in-one-bar must have been doing some strange guessing.)
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