Firefox – How to view a PDF in Firefox when the server specifies the wrong content type

firefoxmime-typespdf

I am using Mozilla Firefox with a PDF viewer plug-in. The plug-in has been correctly associated with Adobe Reader files to view them in the browser in the settings.

I would like to be able to view PDF files in Firefox rather than downloading them. This already works correctly when a web server indicates that a file has the Content-Type of application/pdf. However, some web servers provide other Content-Types for PDFs, such as application/octet-stream. (See this example of a PDF served with a non-pdf Content-Type.)

I have looked at Firefox's MimeTypes.rdf file, and it appears to only support mapping applications based on file extensions for non-Internet-based files. (It looks like it only uses Content-Type to map Internet-based files.)

How can I have Firefox view all PDF documents in-browser rather than only the ones with the application/pdf Content-Type?

Best Answer

Firefox has no content inspection code (e.g. the linux file command) to detect the actual content type and rely on the Content-Type header.

Workaround: `mozplugger` extension

See man 7 mozplugger:

  extensions
          This is a comma separated list of extensions that should be associated with this particular mime type. The  exten‐
          sions are only used when a web server does not report what type of file it is, or when loading files directly from
          disk.

Workaround: human interaction

Save the file and open it in the file explorer ;-)

Workaround: misconfiguration

An additional workaround is to hack mimeTypes.rdf and assign application/octet-stream to the same value as application/pdf.

I don't advice this workaround.

Related Solutions

Word – MS Word 2007+ – can it encode hyperlinks using the PDF Action Type “Launch” instead of “URI” when publising a “.docx” file to PDF

Thank you for your excellent article. It works! Not for me at at first but then I discovered you have to turn off 'protected mode' in adobe X. I don't have this problem at all on adobe 9. It seems to me that the industry is going backwards on functionality in the name of security.

So in Adobe Reader X do:

Make sure open cross docs.. is unchecked. (as you said)
Turn off protected mode: Edit » Preferences » General
Search and replace /Type/Action/S/URI/URI with /Type/Action/S/Launch/F( using a suitable hex editor

There is no easy solution for what we want to do which is allow any user with only a PDF reader with no settings to bother about, to navigate around a folder.
But thanks again for all your work and the light it throws on the subject.

Linux – Fixing Inconsistent Default MIME Type Between System and Mozilla Firefox/Thunderbird

Finally I figured it out: The Mozilla applications are going to look through list of files for mime-type-app associations in following order:

~/.local/share/applications/mimeapps.list
~/.local/share/applications/mimeinfo.cache
/usr/local/share/applications/mimeapps.list
/usr/local/share/applications/mimeinfo.cache
/usr/share/applications/mimeapps.list
/usr/share/applications/mimeinfo.cache
/usr/share/applications/defaults.list

Actually they should not use mimeinfo.cache at all. Because there is no order in these files. In some distro there will be default mimeapps.list which is nice. But many distros does not have default mimeapps.list. In some distro there is no mimeinfo.cache at all. Thus in these distros it falls back to /usr/share/applications/defaults.list which works fine. But in ubuntu, there are still mimeinfo.caches, which will be automatically generated after each updates. In kubuntu it is even worse, because the associations in defaults.list are specified to gnome apps but not KDE ones.

The good way to solve this is to generate my own mimeapps.list and put it into ~/.local/share/applications/.