Download the OpenXML viewer you see at the top of the list here: http://openxmlviewer.codeplex.com/releases/view/25391

For more info, see this article: http://www.theregister.co.uk/2008/12/03/microsoft_ooxml_html_firefox_viewer_interoperability/

I tried this, but I could not get it to work. It is probably my fault. I evidently do not know enough to install the program properly. I also do not want to spend the money or take the time to get someone else to help me. I do not have this problem with windows explorer. Why should I spend several frustrating hour trying to make Firefox work? With a Microsoft or Windows update all you have to do is click on install, the computer works for a few minutes, the installation is complete and everything works. I like the Firefox browser. Have you considered "Firefox for Dummies" instructions?