EDIT: Tried it again on July 1st and it's working again. This is one of those extensions that, in addition to being incredibly useful, shows the potential of Mozilla's Firefox platform and the ingenuity of the developers who write gems of addons like this one. Thank you for your time and effort!
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I hate like heck to write a bad review for such a useful tool, but a couple of days ago, it just stopped working. All results now display simply "no definition found". Five stars easy when it's working.