Seems to work ok in 5.0.1 Rated 5 out of 5 stars

I updated the rdf file (Google "edit an xpi file") to max version 9.9 and it appears to work just fine in Firefox 5.0.1 on my new Windows 7 64-bit machine. This is great news since I love this add-on, especially that it duplicates the history of the tab as well.

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