If you use Office 2003 or Office 2007 and want to use Office Web Apps from Firefox then you are lucky because recently Microsoft released Office Web Apps Browser Plugin that enable Mozilla Firefox to open Office documents directly into the desktop version of the application, make changes and save it back at the web.
It supports Office 2003 SP2 and Office 2007 SP2, Word Web App, Excel Web App and PowerPoint Web App. Mozilla Firefox is supported from version 3.5 and higher.
Office 2010 users don’t need this plugin because Office 2010 already has it.
Grab it immediately here and start enjoying Office Web Apps from Firefox right now!