FireFox how to change print program ???

[clemens at dwf.com]

Firefox has some nice options for printing, but I dont see how
to change the print program itself (lpr).

What I WANT to do is to get things to print double sided (duplex).

What I have done in the past is to tell Mozilla that the print
program was 'ipr' rather than 'lpr' and use this as a filter
to affix 
        << /Duplex false >> setpagedevice
near the top of the postscript output.

So, how do I change the print program (from lpr) in Firefox?
-or-
Is there a better way?

-- 
                                        Reg.Clemens
                                        reg at dwf.com