Thread:Project:Support desk/View Excel/Word documents in browser (2)/reply

That depends on your browser: To open a certain file type in your browser, you need a plugin for the browser, which allows you to open these files. So to open Excel and doc files, you need a plugin, which can open these files. I guess there might be one coming with Microsoft Office.

Note that PDF files are a special case: Normally you would need a plugin there as well. However, if you are using the newest version of Firefox, then you can always open PDF files in the browser (also without any special plugin), because Mozilla integrated a PDF viewer in Firefox.