Hi!

I'm sorry to read that. It could be related to the new built in PDF reader. Take a look to this article to learn more about how to troubleshoot it:

View PDF files using Firefox’s built-in viewer

My other suggestion is to launch Firefox in Safe Mode to make sure that no add-on is interfering with the expected behavior of your browser:

Diagnose Firefox issues using Troubleshoot Mode

Let me know if this works, Ibai

Current Firefox versions have enabled a built-in PDF Viewer that doesn't have all features that other PDF readers like the Adobe Reader have or may not function properly otherwise.

You can change the action for Portable Document Format (PDF) from Preview in Firefox to use the Adobe Reader or set to Always Ask in "Firefox > Options/Preferences > Applications".

You can set the pdfjs.disabled pref to true on the about:config page to disable the build-in PDF viewer.

You can check the value of the plugin.disable_full_page_plugin_for_types pref on the about:config page and remove the application/pdf part if present or reset the pref to the default via the right-click context menu.

See also:

• https://support.mozilla.org/kb/view-pdf-files-firefox-without-downloading-them