Comment 11 for bug 512937

Ran into the issue again with updating to FF 3.6.6.

Setting up firefox (3.6.6+nobinonly-0ubuntu0.10.04.1) ...
update-alternatives: error: alternative path /usr/bin/firefox doesn't exist.
dpkg: error processing firefox (--configure):
 subprocess installed post-installation script returned error exit status 2

The problem is from the previous symlinks:
$ ls -al /usr/bin/firefox
lrwxrwxrwx 1 root root 33 2010-04-27 12:09 /usr/bin/firefox -> /usr/lib/firefox-3.6.3/firefox.sh

and

$ ls -al firefox.ubuntu
lrwxrwxrwx 1 root root 31 2010-06-29 20:35 firefox.ubuntu -> ../lib/firefox-3.6.6/firefox.sh

So I rm'ed /usr/bin/firefox and
$ sudo mv /usr/bin/firefox.ubuntu /usr/bin/firefox
$ ls -al fire*
lrwxrwxrwx 1 root root 31 2010-06-29 20:35 firefox -> ../lib/firefox-3.6.6/firefox.sh

Following that the upgrade to 3.6.6. worked.
Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.6) Gecko/20100628 Ubuntu/10.04 (lucid) Firefox/3.6.6