Mozilla Firefox (or simply Firefox) is a free and open-source web browser developed by the Mozilla Foundation and its subsidiary, the Mozilla Corporation. Firefox is available for Windows, macOS and Linux operating systems, with its Firefox for Android available for Android (formerly Firefox for mobile, it also ran on the discontinued Firefox OS); where all of these versions use the Gecko layout engine to render web pages, which implements current and anticipated web standards. An additional version, Firefox for iOS, was released in late 2015, but this version doesn't use Gecko due to Apple's restrictions limiting third-party web browsers to the WebKit-based layout engine built into iOS.