On his blog: http://cookingwithlinux.com/content/passages#comment-126 John Kerr has mentioned some Firefox add-ons.

One of the one's I like is http://www.wired-marker.org/en/help_basic_operation.html Check it out.

You can highlight parts of a webpage and then it saves the page so you can come back to it. Along with Zotero, which John mentions, this is one of the best extensions for research purposes. (I don't work for, own, have shares or otherwise benefit from telling anyone about this...kickbacks would be nice)
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