Install Firefox 5 Beta in Ubuntu from the Firefox Next PPA

Not long ago Mozilla changed the release cycle of Firefox, so that major new versions (Firefox 5, 6 and so on) will be released every 2-3 months. Currently, the latest alpha release is Firefox 6 Aurora, while the latest beta development version is Firefox Beta 5, which has made it into the Firefox Next PPA already. Installing this version should be very easy if you follow the next steps.