Di Yarrall Rated 5 out of 5 stars

That's strange, because I had no problems. In the author's page http://piro.sakura.ne.jp/xul/_rewindforward.html.en you should push the "Download" item (second from the top), and be passed to the page http://piro.sakura.ne.jp/xul/_rewindforward.html.en#download / There you push the item "Non-secure Download", and from the page http://piro.sakura.ne.jp/xul/xpi/confirm.cgi?rewindforward.xpi you install the extention. If FF will try to block the installation, allow it forcibly.

This review is for a previous version of the add-on (2.1.2009072703).  This user has other reviews of this add-on.