[6][7] Its predecessor, Focus by Firefox, was released in December 2015 as a tracker-blocking application which worked only in conjunction with the Safari mobile browser on iOS.

[12] The version released for German-speaking countries has telemetry disabled and is named Firefox Klar to avoid ambiguity with the German news magazine FOCUS.

[13][14] Firefox Focus is designed to block online trackers, including third-party advertising, with the end goal of both improving browsing speed and protecting users' privacy.

[18] 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.

[19] On iOS devices, Firefox Focus uses the WebKit engine as required by Apple for all browsers on the App Store.

Pressing the trash icon while browsing will delete all session data, and return to the start screen (i.e. display the customisable search bar).