Mozilla has recently introduced a new IonMonkey rendering engine, which is used in their desktop and Android versions of Firefox. Mozilla has previously shown a prototype browser for iOS, called Junior, which used Apple's UIWebView rendering component, before saying: "There are a lot of reasons we should be on iOS even though we can't bring our rendering engine there."
Mozilla is currently facing the same problem on Windows RT, where Microsoft doesn't allow access to Win32 APIs, which prevents them from introducing their own rendering engine and achieving the speed of their OS X and Windows 8 versions. [Update: As a reader has pointed out, Windows RT does not include Win32 APIs.]
Mozilla recently announced Firefox OS, which may help them regain their foothold in the browser market, especially on mobile. Safari currently rules the roost, with Android's native browser coming in second, while Firefox has failed to build a strong presence on mobile.
Source: CNET | Image via Mozilla