and "it" upgraded IW and all the dependencies:
ii xulrunner-1.9.1 1.9.1.11-1~bpo50+1 XUL + XPCOM application runner
I had iceweasel 3.5.10-1~bpo50+1 already installed; what I was trying to
do was upgrade xulrunner from 1.9.1-10-1~bpo50+1 to 1.9.1-11-1~bpo+1.
I finally was able to do so by running command 'aptitude install
xulrunner-1.9.1/lenny-backports', which upgraded xulrunner-1.9.1 and one
of its dependencies. It was important to include the '-1.9.1' in the
package name. I could also have used apt-get instead of aptitude.
I then was able to install all the other pending 26 package upgrades.
Thanks for the tip.