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When using Firefox, PDFs won't load natively on Mac Mountain Lion (10.8.2), even when all add-ons are disabled. No issue using Firefox on PC


Whenever I click on a web link, do download a PDF form, for example, I get this error message:

"We are sorry, but Adobe Reader is unable to show documents in this browser configuration.

Please use your browser to download this file and open it in Adobe Reader or Adobe Acrobat.

To avoid this message in the future, many browsers provide a way to turn off certain add-ons, and some are able to show this document natively. Please contact your browser vendor for more details."

This problem only manifested recently. I have recently added Adobe CS6, but the problem manifests itself even when this is disabled. Any help much appreciated.

Additional System Details

Installed Plug-ins

  • Shockwave Flash 11.5 r502
  • Displays Java applet content, or a placeholder if Java is not installed.
  • Adobe® Acrobat® Plug-in for Web Browsers, Version 11.0.01
  • Simple plug-in
  • The QuickTime Plugin allows you to view a wide variety of multimedia content in web pages. For more information, visit the QuickTime Web site.
  • Microsoft Office for Mac SharePoint Browser Plug-in


  • User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:18.0) Gecko/20100101 Firefox/18.0

More Information

  • Top 10 Contributor
  • Moderator
10738 solutions 96600 answers

The Adobe Reader plugin may not be working properly on Mac.

Disable the Adobe Reader plugin in Firefox (Tools > Add-ons > Plugins) and use the external Adobe Reader application or Preview application instead.

PDF files may be found under entries like Portable document or Adobe PDF document.

  • Firefox > Preferences > Applications > Adobe PDF document : Use Adobe Reader

Question owner

Thanks to you, Cor-el, for the advice. Issue sorted. Disabled the Acrobat plugin as suggested. I see that it is known to cause instability.