dpkg does not automatically remove conffiles on upgrade when a package
stops shipping them.  iceweasel needs to clean up the obsolete conffile
/etc/iceweasel/iceweaselrc in its maintainer scripts, using
dpkg-maintscript-helper.  Please see the manpage of
dpkg-maintscript-helper for details.

Thanks,
Josh Triplett

Hi all,
The obsolete conffile bug is still present in iceweasel 19, any update
on this will be nice.

$ adequate iceweasel
iceweasel: obsolete-conffile /etc/iceweasel/iceweaselrc

Looking forward to the fix.

src:iceweasel has been superseded by src:firefox-esr in version
45.0esr-1 in March 2016. Transitional packages to ease upgrades were
provided in the wheezy, jessie, stretch and buster releases. The
transitional packages have been removed finally before the bullseye
release in August 2021.
After regular security support for buster ended in August 2022 and LTS
support ended in June 2024, I'm closing the remaining bug reports now.

Andreas