It's basically the same as using a top load machine, with a couple of twists.
The agitation in a top loader is caused by the back and forth motion of the middle section. The agitation process for felting in a front load washing machine is caused by the rotation of the drum. This rotation causes the project to be dropped from top to bottom of the drum repeatedly as the machine goes through the washing process.
Another difference between using a front loader and a top loader for your felting projects is that front loaders usually lock shut during a cycle. This means that you can't stop the wash mid-cycle and open the door to check on your project like you can in a top loader.
Some front loaders allow you stop the cycle and drain the water as soon as the wash part is done. You have to be on the spot and catch it before the spin starts, drain the water then remove your piece and rinse it by hand.
That may sound daunting, but if you've done your homework and tested your swatch, as I recommend then you should have no problems.
Here's what you should do to ensure a good felting experience...
If your machine does not allow you to stop mid-cycle, then you have no choice but to go through the spin cycle too. In this instance I'd suggest that you only use bulky yarn, as allowing some finer yarn projects to spin after felting can cause creasing which cannot be removed.
So - felting in a front load washing machine truly is possible, but make sureyou do exactly the same process with your swatch as with your finished item. That includes doing EVERYTHING the same...using the same size hook, same yarn, same cycle and measuring all the way. See my felted crochet page for more information on which measurements to take.
So - I hope you enjoy felting in a front load washing machine. Try it - take the plunge.