Firefox Focus

Firefox Focus is a free and open-source privacy-focused mobile browser from Mozilla, available for Android and iOS smartphones and tablets. Firefox Focus was initially a tracker-blocking application for mobile iOS devices, released in December 2015. It was developed into a minimalistic web browser shortly afterwards. However, it can still work solely as a tracking-blocker in the background of the Safari browser on Apple devices.
In June 2017, the first release for Android went public and was downloaded over one million times in the first month. As of January 2017, it is available in 27 languages. Since July 2018, Firefox Focus is preinstalled on the BlackBerry Key2 as part of the application "Locker".
To bypass content-blocker restrictions from Apple, Firefox Focus uses the UIWebView API on iOS devices. On Android, it has been using the Blink engine in version 6.x or earlier, and GeckoView since version 7.0.
Tracking protection.
Firefox Focus is designed to block online trackers, including third-party advertising, with the end goal of both improving browsing speed and protecting user's privacy. Content blocking is achieved using the Disconnect block lists. The blocking of third-party trackers (except "other content trackers") is enabled by default. In the other Firefox browsers, users have to enable the Tracking Protection feature inside the browser preferences manually. Users can also view types of trackers on a page by tapping on the shield icon next to the URL bar. A panel will pop-up and shows what kind of trackers are on that page: ad trackers, analytics trackers, social trackers or content trackers.
On December 20, 2018, Mozilla announced that Firefox Focus now checks all URLs against the Google Safe Browsing service to help prevent people from accessing fraudulent sites.
Functions.
Firefox Focus can be set as content-blocker in the Safari web browser options. After activating the Safari integration in the Firefox Focus settings, it will disable trackers automatically in the background when browsing using the Safari browser.
Pressing the trash icon while browsing will delete all session data and refer to the startscreen, that is displaying the customisable search bar. Tabs can be opened by long-pressing a URL on a website. Favourite links can be set on the homescreen of the device.
Firefox Focus contains a option called telemetry. By activating it, users allow Mozilla to collect and receive non personal-identifiable information to improve Firefox. Due to privacy concerns, telemetry of Firefox Klar is disabled by default.
October 15, 2018, Mozilla announced that Firefox Focus is being updated with a new search feature and visual design. That means the browser will conceptually tell users about its features and options. 
Minimum device requirements.
Apple mobile devices.
There are some minimum hardware requirements to remove tracking contents. The mechanism needs hardware that can handle the extra load of content blocking so it only works on 64-bit devices running iOS 9 and above including:
, iOS 11.4 or above is required to download Firefox Focus on the App Store.
Android mobile devices.
Android version 5.0 or higher is required to use the latest version of Firefox Focus.
Firefox Klar.
"Firefox Klar" is the modified version with telemetry disabled released for German-speaking countries in order to avoid the ambiguity with the German news magazine "FOCUS". F-Droid uses this flavor due to telemetry being disabled by default in Klar.