Opening PDF files within Firefox

I can't open pdf files side Firefox recently. I am using Firefox 3 on Windows XP.

After done some googling, I found
Opening PDF files within Firefox which provides a complete solution of this problem. The following method works for me.

   1. Close Firefox.
   2. Navigate to my Firefox profile folder.
   3. Delete the mimetypes.rdf file.
   4. Restart Firefox.

For how to find profile folder, refer to to How to find your profile.