For those who are using Firefox as web browser, you may already have experienced some issue with SharePoint functionalities.
One of this issue may be with Office Web Apps.
Now, be happy , Microsoft has released a plug in which make Office Web Apps working with Firefox (you need Firefox 3.5 or later)
You don’t need it if you have Office 2010 installed, as this is already included on Office 2010.
If you have Firefox and either Microsoft Office 2003 or Office 2007, this plugin enables you to open documents directly from Office Web Apps into the appropriate Office desktop application. For example, in Word Web App, clicking Open in Word results in the document being opened in Word 2003 or Word 2007. When the document is saved in Word, it is saved back at the web location where it was opened.