I've been using pdf.js in Firefox for some time (Firefox 38.0.5 currently and Windows 7) and pdf.js was ok. However lately, I noticed that pdf.js isn't being opened anymore and instead nothing happens.
I dediced to go into my Applications and set so it never opens in PDF.js However I noticed this:
To make matters worse, the settings displayed on picture, aren't applied until PDF.js is uninstalled.
I'd like to keep PDF.js for PDFs, but I haven't found a solution.
EDIT: A synced version of Firefox 38.0.5 on Windows XP works fine. Additionally I attempted to refresh Firefox and it didn't work, although the screeenshot from above only shows one file type.