After I download a file, Firefox will present an "Opening" dialog, with an "Open with" drop-down list, where I can choose from the last two applications I used or specify "Other...". I regularly switch between more than two different external applications for viewing the same file type (I open PDFs with evince, Acrobat Reader, or Mendeley Desktop depending on the same circumstances). How can I make the drop-down list display the last three applications instead of the last two? I previously asked this question on Super User but received no response: http://superuser.com/questions/703286/more-than-two-helper-applications-in-firefox-open-with-drop-down-list