How to install helper applications

I use Galeon 1.3.20 on Debian Sarge. My window manager ist fvwm2. (I
know of the newer versions of galeon.)

I used to use Acroread for viewing pdf files when browsing, but want to
change to xpdf.

My steps:

* uninstall Acroread as plugin.
* install xpdf
* searching for installation of xpdf as default helper application
  whenever pdf is to be displayed within/out of the browser.

So far when linking to a pdf file galeon offers an alert of two
helper application to choose of, one of which is xpdf (the other acroread).

I want to eliminate this step: when linking to a pdf file galeon should
start xpdf without asking me.

Installation of such defaults used to be an option in the menu called
'helper application' or, perhaps, 'mime types'.  How is it done now?

The above question is not restricted to xpdf but concerns every helper
application.

Additional question: is xpdf installable as a plugin?


I know of:

        gconf-editor
        about:config
        about:plugins

That does not seem to be enough.

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