TechWeekEurope has a whole gallery of the OS, which you can see at the link below. Mozilla believes the OS will be lighter and faster, while being more open than Android.
The OS is intended to be loaded on low end smartphones, however the OS has support for many smartphone features such as including calls, texts, web browsing, calendar, and contacts. Looking at the screens, there are definitely similarities from other mobile operating systems such as iOS, Windows Phone, and Android.
With all applications written in HTML, Mozilla hopes to win over developers by being an easy platform to develop on.