You posted this thread in the Firefox for iOS section and not in Firefox or Android Firefox. The Firefox shell browser for iOS devices (neededing iOS 8.2 at minimum) is still pretty new so the browser versions is not the same as the desktop and Android Firefox. The Firefox shell for iOS only first came out back in September 2015 in New Zealand iOS app store in testing and then for many other markets on November 12, 2015 which is why it has a low version number of 5.2 currently. Besides the iOS version is not using the Gecko and JavaScripts engines the desktop and Android Firefox uses due to Apple restrictions.