Make sure the server is sending the correct MIME type: application/pdf. You can analyze the Content-Type server response in the Web Console (Ctrl+Shift+K) to find out which MIME is sent.

• https://developer.mozilla.org/en-US/docs/Tools/Web_Console

Why are you using such an old version of Firefox? Apart from all the security vulnerabilities that have been fixed, in recent versions there's no need to disable the built-in PDF reader: you can just select an action for PDF files under Options - Applications.
It looks like you're using Firefox on Solaris in a university environment. You can find the current ESR release below:

• ftp://ftp.mozilla.org/pub/firefox/releases/24.3.0esr/contrib/

Thanks for the information about the ESR-Version. But the Problem is not the built-in PDF reader. I have made a few screenshots to discribe the Problem bether:

In Firefox 18.0.2 the Window shows our Standard application. If I browse for an other Program and open the pdf, the searched program becomes the new default Option.

In Firefox 27.0 (and 22 or something like that was the same) the Window doesn't remind the choices. The it's allways "Save File" Selected. It doesn't display the name of my last decision for the "Open with:" Option.

Thanks for your fast answer and Sorry for my bad English. I hope these screenshots makes the Problem clear. The MIME-type of the file is application/pdf. It works with the older FF but does not work with the new one.

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 if you want to display PDF documents in Firefox with another application (i.e. not the built-in PDF Viewer).

• http://kb.mozillazine.org/about:config

I had changed the plugin.disable_full_page_plugin_for_types pref before, but it doesn't solve my Problem. We use a pdf-reader that is not a plugin for firefox. I don't know why firefox works so different since the built-in PDF-reader has been added. I have the same Problem with other MIME types as well. E.g with .doc files there is the same Problem. It works on Solaris with Version 18.0.2 and lesser. Doesn't work with a greater FF Version.

I will try the latest ESR Version, maybee it will fix the Problem.

Is the file in your screenshot publicly accessible? If so, can you post a link to it?

In your first screenshot, the file is identified as a PDF Document. In the second, it's identified as PDF Data.
Have you tried checking the "Do this automatically…" option (Für Dateien dieses Typs…), selecting Open With (Öffnen mit) and manually choosing the PDF reader application? Once you do that and click the OK button, you should have a new PDF entry under Options - Applications.

The File is just a test pdf file on our Web host. But The Problem is not the file. It's the same if you use this. Random test file. Before the update, Firefox also just picks the MIME defaults from "~/.local/share/applications/". After the Update, firefox just don't use this MIME database anymore (i think this is the main problem)

>>"Have you tried checking the "Do this automatically…" option (FürDateien dieses Typs…), selecting Open With (Öffnen mit) and manually choosing the PDF reader application? Once you do that and click the OK button, you should have a new PDF entry under Options - Applications. "

There is only one application/pdf entry in the menu. I have tried it but than happens the Display error. We need the Option for our users so they can download and open the file. My Programm is listet in the menu, but if i choose to "allway ask" the Programm is not shown at the "Open with" point. The Option "Open with" is selectet BUT it looks like no Programm is chosen(in german "Durchsuchen..."). If i just Press "OK" and don't choose a Programm, it will start the Programm listet in Options - Applications. If no Programm is chosen i should normaly get an error ("" can't be chosen" or something like that). Hmm PDF-File and PDF-Document can just be a changed name in the firefox description.

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 if you want to display PDF documents in Firefox with another application (i.e. not the built-in PDF Viewer).

You can try renaming mimeTypes.rdf in the profile folder while Firefox is closed. Everything under Options - Applications will be reset to the default.

• Profiles - Where Firefox stores your bookmarks, passwords and other user data

If that doesn't help, then I have no further suggestions. You may have hit a bug. Though from the sound of it, it's mostly a cosmetic issue, since you can just click OK to open the file with the associated application.

• https://developer.mozilla.org/en-US/docs/Mozilla/QA/Bug_writing_guidelines

ub.uni-tuebingen wrote:

Random test file.

That link has the proper MIME type and no Content-Disposition header. When I click it, the download prompt properly labels the file an "Adobe Acrobat Document" and Adobe Reader is the suggested application.

ub.uni-tuebingen wrote:

Hmm PDF-File and PDF-Document can just be a changed name in the firefox description.

On Windows at least, the file descriptions come from the operating system, not Firefox.