Open IT Online, an add-on for Firefox, delivers you what you want.  Well, it delivers you what you want, if you are one of those people who love all these new Online services such as Zoho’s office applications or Google Docs.  Open IT Online allows you to open your documents and images online without the need of any software to be installed.
Here are some of the extension types it can recognize and handle:

Documents (*.doc, *.rtf, *.odt, *.sxw)
Spreadsheets (*.xls, *.csv, [...]