Brian D. Hicks writes:
 > After my last apt-get dist-upgrade on my Debian testing box, I ran into
 > a peculiar effect when attempting to view PDFs with mozilla.  Even
 > though my preferences specifically say to view all PDFs using xpdf,
 > mozilla attempts to load acroread anyway (and acroread promptly crashes
 > or just quits, I'm not exactly sure).
 > 
 > Uninstalling acroread seems to solve the problem, but I still wonder 
 > why mozilla overrode my preferences like that.

Is it possible that you have plugger installed?  Plugger came along
with mozilla on my Mandrake install:

       Plugger is a  Netscape plugin which can show many types of
       multimedia inside your Netscape. To accomplish this, Plug­
       ger  uses  external  programs such as xanim, mtv, timidity
       and tracker.

       For up-to-date information on  Plugger,  see  the  plugger
       home page: http://fredrik.hubbe.net/plugger.html

If you do have plugger, take a look at /etc/pluggerrc.  Mine looks
like this:

application/pdf: pdf: PDF file
application/x-pdf: pdf: PDF file
text/pdf: pdf: PDF file
text/x-pdf: pdf: PDF file
        repeat swallow(documentShell) fill: acroread -geometry +9000+9000 -xrm '*userFrontEndProgram: FALSE' "$file"
        repeat swallow(gv) fill: gv -safer -quiet -antialias -geometry +9000+9000 "$file" 2>/dev/null
        repeat swallow(xpdf) fill: xpdf -g +9000+9000 "$file"

which means that plugger will first try acroread, then ghostview and
finally xpdf.  You can change your pluggerrc to make this work the way
you want.  

Hope that helps, 
r