Here are some of the extension types it can recognize and handle:

• Documents (*.doc, *.rtf, *.odt, *.sxw)
• Spreadsheets (*.xls, *.csv, *.ods, *.sxc)
• Presentations (*.ppt, *.pps, *.odp, *.sxi)
• Images (*.jpg, *.gif, *.png)

How do you use it?  Well whenever you face a document with the “Open With” option, it will also give you the option to open it Online.  From there you can choose one of the various Web 2.0 tools to view and edit the document in question.

One last really nice feature is that Open IT Online gives you the ability to also see the file size of the document you are about to view.  This is handy in determining if you want to open the file, or not.

You can pick up the Open IT Online extension from the Firefox Add-ons site or learn more about it at OpenItOnline.com.