One reason given by Mozilla was that prior to iOS 8, Apple had supplied third-party browsers with an inferior version of their JavaScript engine which hobbled their performance, making it impossible to match Safari's JavaScript performance on the iOS platform.[182] Apple later opened their "Nitro" JavaScript engine to third-party browsers.[183] In 2015, Mozilla announced it was moving forward with Firefox for iOS, with a preview release made available in New Zealand in September of that year.[184][185][186] It fully released in November later that year.[187] In November 2016, Firefox released a new iOS app titled Firefox Focus, a private web browser.[188]