Rated 5 out of 5 stars
This works great to enable Firefox's internal rendering capability for PDF's where the site sends Content-Disposition: attachment. One of my must have add-ons.
Rated 2 out of 5 stars
Works sometimes. I have a financial site that uses Content-Disposition = attachment for pdf files. It also uses Content-Type = Application/pdf.
Even with this add-on, for this site FF asks me to save the pdf and does not display it in FF.
Note: that in Preferences > Applications "Display in Firefox" is selected.