Install Firefox 15 in Ubuntu 11.04 and 11.10

To install or update Firefox 15 in Ubuntu 11.04 and above versions, one has to download the code from the Mozilla Firefox site. To install latest Firefox in Ubuntu 11.04 and Ubuntu 11.10 open the terminal and type the following command.

$sudo add-apt-repository ppa:ubuntu-mozilla-security/ppa
$sudo apt-get update
$sudo apt-get install firefox

The following commands will install Firefox or if you had previous version of Firefox then it will be updated to Firefox 15.

Firefox can be installed in Ubuntu  also using Synaptic manager.
Open the synaptic manager and search for Firefox and install it.
As Synaptic manager is not installed by default in Ubuntu 11.10 see here
How to install synaptic manager in Ubuntu 11.10