The site is http://www.yourfirefoxaddons.com. If you attempt to download the add-on, you get a hash error. I need both links (the one at the top of the page, and the one at the bottom) to function properly asap.
I don't think there is any issue with your extension. You should rename the 1st downloadable to topsellers.xpi instead of zip. It installed fine on my firefox 2. In which version you get the error?
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I have already solved your problem. I have tested the installation from one of my websites. If you PM me, I can send you screenshots of the fixed extension as installed in my Firefox. PM me for more details.