The app currently supports the Firefox browser, as well as the Firefox browser on Android. Firefox OS is not yet supported, due to a scrolling error that we cannot fix without having an actual device. We are working to solve this, but in the meantime you can get the app at the source link below.
If you are in Firefox, click the link and click the big blue Install button. Once the application is installed, the page will tell you where you can find the app. We are happy we finally get to extend the app love to our Firefox users, and hopefully Firefox OS devices once we iron out the bugs. You can get the app at the below source link.
Source: Firefox Marketplace