Is that with uploading a file to the server or with the server sending the PDF file to Firefox.

In case of the latter you will have to configure the server to send the file with the correct application/pdf content type.

• https://developer.mozilla.org/en/docs/Properly_Configuring_Server_MIME_Types

Thanks for the help but think that this is not the problem. Only when I send for Firefox is what happens. If sent by IE no longer have problems.

Can you post a link?

IE usually does content sniffing to see which file is received, but Firefox require the correct MIME type and will display the file as text if the server sends the file as text/plain as many servers do in such a case.

You can check the HTTP response headers with the Live Http Headers extension.

• Live Http Headers: https://addons.mozilla.org/firefox/addon/live-http-headers/