Ubuntu Linux has a default browser functionality that will automatically launch the correct browser when clicking on a link in a gnome gui application. It's easy enough to set the default browser using the GUI tools, but sometimes it's easier to set it using the command line client.. for instance, if you are trying to remotely administer a machine.
To change this setting, we'll use the update-alternatives command.
sudo update-alternatives --config x-www-browser
You should see something similar to this. You'll notice that konqueror is the default browser on my computer right now.
$ sudo update-alternatives --config x-www-browser
There are 2 alternatives which provide `x-www-browser'.
Selection Alternative
-----------------------------------------------
1 /usr/bin/firefox
*+ 2 /usr/bin/konqueror
Press enter to keep the default[*], or type selection number:
If I wanted to select firefox as the default browser, I could just type 1 and hit enter.