Forget MS Office 2007, now you can open docx files in Firefox. Firefox is quite faster in opening a docx file than Office 2007 itself thanks to OpenXML Viewer add-on. It is available for both Windows and Linux.
This add-on lets you open docx files inside Firefox just like any HTML webpage. The best thing is that it retains both the layout and the text formatting.
The installation of this add-on is slightly different, once you have downloaded the zip file, extract it anywhere. Inside the folder you will see OpenXMLViewer_win_firefox.xpi file if you are using Windows, open this file using Firefox. It will now ask weather the extension should be installed, click Install Now button. Once the installation is complete, restart your browser.
If you are looking for a way to install it in Linux, check out ReadMe file inside the folder.
Once the plugin is correctly installed, navigate to Tools > Options > Applications tab. For the content Microsoft Office Word Document, choose Use OpenXMLViewer as shown in the screenshot below.
Once this is done, now you will be able to open any docx file in Firefox. An example of a docx file opened in Firefox is shown in the screenshot below.
Note: It only opens .docx file not .doc file. Also note that you can only view the content, not edit any of it.