Users don't have to do anything special, they just have to hit the install button
It seems that Ubuntu is capable of running applications destined for Firefox OS without any kind of tweak or intervention from the users.We tested Ubuntu 14.04 LTS Beta (Trusty Tahr) with the Firefox Marketplace and we managed to get a few games and applications running. To top things off, users can even lock the apps to the Unity launcher, making them permanent.
How is this possible, you might ask? Well, Ubuntu supports HTML 5 apps, and if you remember correctly, the distribution already comes with a number of them installed. When you first open Ubuntu after a fresh install, you will notice an Amazon icon, for example. If you click it, you will be sent to a website.
In this case, the so-called Webapps are nothing but some glorified bookmarks. The only advantage is that they can be launched from outside of a browser. Firefox OS only works with Webapps, and this means that Ubuntu will also be able to run some those apps.
This is nothing more than a curiosity and it's likely that Mozilla might clamp down in the future on this particular functionality of the marketplace. Webapps never really took off on the desktop platform, but you can try them for fun.