Just a quick note: After updating to Kubuntu 11.10 today, Firefox didn’t startup anymore and the console told me:
mattanja@tiger:/opt$ /opt/firefox/firefox bash: /opt/firefox/firefox: No such file or directory
Obviously it’s a bug: https://bugs.launchpad.net/ubuntu/+source/ia32-libs/+bug/852101?comments=all
The workaround & fix is to reinstall libc6-i386:
apt-get install --reinstall libc6-i386