After upgrading from Dapper Drake to Hardy Heron I decided to keep using Firefox 2 rather than Firefox 3, even though the latter had been installed - no problem.
However, a few annoying problems with Firefox 2 prompted me to make the switch. So, I ran
sudo update-alternatives --config x-www-browser
to set Firefox 3 to the default web-browser and uninstalled the firefox-2 package. However, clicking on the Firefox icons continued to run Firefox 2.
After digging around I realised that I still had a local copy of the Mozilla Firefox 2 build due to having used ubuntuzilla. To fix this I did the following: