POPART  Headup is a great addon for Firefox to use in context with your Tweeting activities. It makes easy work out of discovering more about fellow "tweople" by snooping their social profiles & displaying them above your Twitter browser tab in an overlay interface.

Check out this blog post by Jeff Pulver on the subject, includes full "how-to": http://pulverblog.pulver.com/archives/008842.html  
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