First off, this issue started Monday, August 25th 2014 when I was forced to update Firefox in order to log into my online accounting program. I was not having this issue in the previous Firefox version. When I open a PDF document from an email (which shows a Firefox icon next to it), the document opens in Adobe reader, but also a blank tab opens in Firefox, even with it's not already open. When I close the PDF document, the Firefox tab remains open and I have to manually close it. This does not happen with PDF documents that I have saved to my company's network or to my computer (which have the Adobe icon). I refuse to have to save PDFs to my computer as a workaround for this issue. Under Tools > Options > Applications, I've already switched the Adobe/PDF options to open in Adobe. Also, in about:config, the value for "pdfjs.disabled" reads "true" and "plugin.disable_full_page_plugin_for_types" contains "application/pdf". I work with a lot of PDFs and I'm frustrated to the point where I'm about to unistall Firefox and just use Internet Explorer.