OpenXML is a free and open standard from Microsoft. MS Word 2007 document files are stored using OpenXML. The OpenXML Document Viewer application was designed to be a browser plugin, that can be used on computers which dont have Microsoft Office 2007, to view the Word 2007 files using just the browser.

The OpenXML Viewer browser plugin translates the Word 2007 file into HTML so that it can be viewed on a browser. Once the plugin is correctly installed, navigate to Tools>Options>Applications tab in Firefox.