Do this automatically is linked to a specific MIME (content) type and not to a file extension. So this will only work properly is this is a file that is send as application/pdf.

You can check the mimeTypes.rdf file in the profile folder to see what this entry looks like.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

I'm afraid this is way above my level of expertise. Sorry.

When I open a .pdf document a pop-up asks what Firefox should do with this file. I select "Open with Foxit Reader 8.3 (default)". I then check the box instructing FF to "automatically open files like this with Foxit from now on". The problem is that this doesn't work and the pop-up appears each and every time I open a .pdf document. Can this be fixed by Mozilla? Thanks.

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Here are my current application settings:

Foxit PPDF document Use Foxit Reader 8.3(default) Foxit Reader FDF document Use Foxit Reader 8.3(default) Foxit Reader PDF document Use Foxit Reader 8.3

I can find no way to make the third item, a PDF document a default in the applications settings although, when the pop-up happens with a PDF document, this, Use Foxit Reader 8.3(default), is displayed. It's very confusing.

BTW, I have no idea what a PPDf or FDF file is.

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irishmist20 said

Here are my current application settings...

There should be a standard description that just says Portable Document Format (pdf) and doesn't mention Foxit. Do you have that one? It's the one pictured in this article: View PDF files using Firefox’s built-in viewer.

Is Firefox not following that preference?

Try reading through this support article. A few members solved the same issue with help from other members. Looks like you may have to change some settings within Foxit.

https://support.mozilla.org/en-US/questions/759828

SUCCESS! When I visited Options>Applications I saw only the first three items:

Foxit PPDF document Use Foxit Reader 8.3(default) Foxit Reader FDF document Use Foxit Reader 8.3(default) Foxit Reader PDF document Use Foxit Reader 8.3

HOWEVER, hiding NINE lines down in the list was:

Portable Document Format (PDF) and I set: Use Foxit Reader 8.3(default)

Problem solved. Every .pdf document opens now in Foxit reader.