From time to time, prior to the release of major new features in Hellfire, these features need to be tested publicly. This is done by offering Hellfire in a sneak preview "pre-release" version which anybody can try out.
Beware that pre-release versions contain features they may not be fully complete, and may suffer from crashes, performance loss, and lockups. You should save your games often, and if you suffer a repeated crash or lockup then sending in the saved game will help to diagnose the problem. Your saved game will also be fixed where possible so you will be able to continue you game.
If you want to take part in testing upcoming features then you can do this at any time. You can also switch back to the stable version of Hellfire (but be aware that saved games or career files saved with a pre-release version may not load under the current stable version).
Switching to the current pre-release version is straightforward; launch Hellfire and select Game Settings.
Tick the option to "Allow Installation of Pre-release Versions" and then select "Check for Updates Now" (Note that you have to check for updates for the first time in this screen otherwise your preference won't be saved).
Hellfire will shut down, and the Hellfire Updater will start, prompting you to download the new version (just as per a normal update).
You will know you are running a pre-release build when you see the build number on the opening screen.
Should you ever want to go back to the stable version, simply uncheck the "Allow Installation of Pre-release Versions" and carry out the above steps; Hellfire will switch back to the stable channel.