I have a fresh Firefox install on a Win7 PC without a dedicated PDF reader. I was under the impression that I don't need to install one because Firefox has a built-in viewer. But if I attempt to open a downloaded PDF, Firefox opens a tab and then apparently decides that it should forward the file to Firefox for opening - which opens a new tab yet again, and this sequence repeats until I close the browser or my PC runs out of RAM.

The setting for content type PDF is set to "preview in Firefox". That works for a subset of files from the 'net (I guess those with an appropriate response header) but fails for downloaded files. What do I have to do to fix this?

Note that installing a dedicated PDF reader is not an acceptable solution. This did work flawlessly without a third party plugin like acrobat or foxit etc on my old Win7 install, but I reinstalled the OS and now it's broken for some reason.

1 Answer 1


I know this is an old question, but I was having the same problem myself today, and this is still near the top of the search results I got.

This worked for me:
Go to ☰ -> Options -> Applications -> Search for the PDF type and set to "Preview in Firefox".

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