I do not see the Adobe Reader (PDF) plugin listed with your original question. To see the plugins submitted with your question, click "More system details..." to the right of your original question post. You can also see your plugins from the Firefox menu, Tools > Add-ons > Plugins. Try the following: #Close all Firefox windows, File > Exit #Click (Windows) Start > All Programs (or Programs) > Adobe Reader (Adobe Reader will open) #On the Adobe Reader menu, click Edit > Preferences > Internet #Under Web Browser Options, check the "Display PDF in browser" box #Click OK. Close Adobe Reader #Restart Firefox and test Also, check your settings for PDF Content type in Tools > Options > Applications (I know you said you have already done this, but check it again after doing the above). See: *http://support.mozilla.com/en-US/kb/Managing+file+types *http://kb.mozillazine.org/File_types_and_download_actions