I don't have an immediate answer for you. Could you save the "working" mimeTypes.rdf file and compare it with a non-working mimeTypes.rdf file? If you do not have a tool you like, I usually use WinMerge for such things.

What I'm curious to know is what PDF-related differences you find in the working vs. non-working files.

I used winmerge to compare the 2 files. What info should I post for you to look at?

I'm interested in the PDF-related differences. I don't know if there is a way to copy them side by side, but you could paste those parts sequentially.

I am noticing that the "bad" file has a lot more entries than the good file for pdf. I can't get them side by side.

Good file <RDF:Seq RDF:about="urn:mimetypes:root">

<RDF:li RDF:resource="urn:mimetype:application/pdf"/>

 </RDF:Seq>

<RDF:Description RDF:about="urn:mimetype:application/pdf"

NC:value="application/pdf"

NC:editable="true"

NC:fileExtensions="pdf"

NC:description="Adobe Acrobat Document">

<NC:handlerProp RDF:resource="urn:mimetype:handler:application/pdf"/> </RDF:Description> <RDF:Description RDF:about="urn:mimetype:handler:application/pdf"

NC:alwaysAsk="true"

NC:saveToDisk="true">

<NC:externalApplication RDF:resource="urn:mimetype:externalApplication:application/pdf"/> </RDF:Description>

Bad file

<NC:externalApplication RDF:resource="urn:mimetype:externalApplication:application/pdf"/> </RDF:Description>

<RDF:Description RDF:about="urn:mimetype:application/pdf"

NC:fileExtensions="pdf"

NC:description="Adobe Acrobat Document"

NC:value="application/pdf"

NC:editable="true">

<NC:handlerProp RDF:resource="urn:mimetype:handler:application/pdf"/> </RDF:Description>

<RDF:Seq RDF:about="urn:mimetypes:root">

<RDF:li RDF:resource="urn:mimetype:application/pdf"/>

<RDF:Description RDF:about="urn:mimetype:application/x-download"

NC:value="application/x-download"

NC:editable="true"

NC:fileExtensions="pdf"

NC:description="Adobe Acrobat Document">

<NC:handlerProp RDF:resource="urn:mimetype:handler:application/x-download"/> </RDF:Description>

<RDF:Description RDF:about="urn:mimetype:handler:application/pdf"

NC:alwaysAsk="true"

NC:useSystemDefault="true"

NC:saveToDisk="false">

<NC:externalApplication RDF:resource="urn:mimetype:externalApplication:application/pdf"/> </RDF:Description>

The main differences I see are:

(1) The options for how to handle PDFs are a bit different:

<RDF:Description RDF:about="urn:mimetype:handler:application/pdf"
  NC:alwaysAsk="true"
  NC:useSystemDefault="true"
  NC:saveToDisk="false">
 <NC:externalApplication RDF:resource="urn:mimetype:externalApplication:application/pdf"/>
</RDF:Description>

(2) An additional PDF content type is defined, which :

<RDF:Description RDF:about="urn:mimetype:application/x-download"
  NC:value="application/x-download"
  NC:editable="true"
  NC:fileExtensions="pdf"
  NC:description="Adobe Acrobat Document">
 <NC:handlerProp RDF:resource="urn:mimetype:handler:application/x-download"/>
</RDF:Description>

There is a bug on file about problems uploading when PDF is associated with the application/download or application/x-download content type, but it isn't solved, suggesting that no one has found the reason for the association.

Is it possible that the user is downloading a PDF that Firefox does not recognize as a PDF (because the site is sending the application/x-download content type), and the user assigned it to Acrobat, and this is how it gets added to mimeTypes.rdf?

Bug 373621 – File upload set mime type as application/download instead of application/pdf

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In this case today, I was the user. I was emailed a PDF, I saved it to my desktop, tried to upload it via FF and got the message the file wasn't a PDF. I deleted my mimetypes.rdf and tried uploading the same file and it worked no problem.

I made no changes to the PDF between the uploads. All I did was save it to my desktop.

The download was just a save without opening?

Can you tell me what email site it was (e.g., Yahoo, Gmail, Outlook/Hotmail, OWA, etc.)?

Just a save without opening from my google apps account. (Web based gmail)