On my site PDF files are used for printing purposes. Starting with v19 visitors start start to claim that this functionality is not working any more. The cause of this is the new built in PDF viewer. It doesn't open print dialog after pdf file download if the the file is built to doing this. Also I’ve found that the quality of printing via the built in viewer is unacceptable. The content is distorted by the JPEG compression and additional headers and footers are present on the page. So for my site built in PDF viewer should be disabled at all. I've found no way to do this at the site level. I think that the instructions for disabling the new feature is too complex for ordinary users and it easier to ask them to use another browser. I think that should be an option at the site level to disable the built in PDF viewer. At least this option should force the browser to ask the user that for working properly with this site the built in PDF viewer should be disabled. And if user choose to disable it this should be done in one click.
Websites can't disable PDF.js, and they never will be able to. The security implications of allowing a website to modify preferences in a browser, set plugins, etc. are immense! Instead, what you can do, is if there are specific issues with your website and PDF.js, please go to bugzilla.mozilla.org, and file a bug report to get them fixed.
You can completely disable pdf.js by going to "about:config" and setting "pdfjs.disabled" to true.
Edit: Reading your post again, I do agree that sites should be able to suggest that Firefox not use the built-in PDF viewer, but I don't know if Firefox has this functionality.
Yes Firefox is as always highly customisable, so users may choose instead to
We document this (and the process to change this was mentioned in a post above)
For anyone having trouble with PDF.js, please try firefox beta, there are some improvements to PDF.js (especially printing) that may make your life easier with it.
The latest version of the PDF viewer is available as an extension and does a better job than the 0.6.143 version shipped with Firefox 19 in a lot of cases.
You can find the latest version of the PDF Viewer (pdfjs) extension here:
FF19 ignores your "Application preferences", described in [https://support.mozilla.org/en-US/kb/change-firefo
Here's a link to EASILY disable the built in PDF viewer. (I tried the 'about:config' & couldn't figure it out)
How to disable the built-in PDF viewer and use another viewer|https://support.mozilla.org/en-US/kb/disable-built