If you want to install Firefox outside of the Linux package manager, below is an explanation of how to do that.
If you want to install the latest Firefox version and keep it up-to-date going forward, rather than relying on the Ubuntu package manager, below are the steps to do that.
Then, unpack the files:
tar xjf firefox-33.0.2.tar.bz2
Next, if you had a previous version of Firefox installed in /opt, remove it:
sudo rm -r /opt/firefox/
Then move the firefox folder that you just unpacked into /opt:
sudo mv firefox /opt/firefox33
Back up your old Firefox launcher and create a symlink pointing to the new Firefox version:
sudo mv /usr/bin/firefox /usr/bin/firefox-old
sudo ln -s /opt/firefox33/firefox /usr/bin/firefox
Now you can run Firefox:
If you would like to create a shortcut to Firefox, navigate to /opt/firefox33 and right-click on the firefox file. Select "copy." Then right-click on the desktop and select "create new launcher here..."
Paste what you copied into the "Command" field (/opt/firefox33/firefox). For name, put "Firefox." Double-click on the image of the launcher and navigate to the Firefox icon:
Now, Firefox will manage all of its own updates independent of Ubuntu's package manager.