As with its desktop version, it uses the Gecko layout engine, and supports features such as synchronization with Firefox Sync, and add-ons.

[19] Plugin support was initially disabled by default, removing compatibility with popular web content types such as Adobe Flash.

[23] On June 27, 2019, Mozilla unveiled Firefox Preview (codename "Fenix"), a redesigned version of Firefox for Android based on GeckoView – an implementation of Gecko that is decoupled as a reusable library, intended to be used as an alternative to the default Android WebView component (based on Blink engine).

[24][25] It has a redesigned user interface with support for dark mode, a new "Collections" feature for saving sets of tabs, and includes Enhanced Tracking Protection (a configurable blocker for web trackers and third-party cookies) and a redesigned private browsing mode.

[32] The stable build of Firefox for Android has general WebExtension support as of version 120; Mozilla announced in November 2023 that all add-ons marked as Android-compatible by developers would be shown on addons.mozilla.org by December 14, 2023.

[37] For operating systems not supported by Fennec, like Sailfish OS (based on Mer project), web browsers can use embedlite (IPCLiteAPI), a lightweight embedding API.

The main criticisms[56] of the browser pre-version 14 were slow browsing speed, lack of plugin support and performance issues.

[57][58] To address these concerns, Mozilla redesigned the browser in version 14.0, adding Flash support, improving start-up speed, as well as other enhancements.

As of September 2014[update], the average user rating of Firefox for Android on the Google Play Store is 4.4.

[61] Despite that, Firefox for Android enjoys a high Play Store rating, has over 100 million downloads,[62][63] and continues to be developed.

[64] In its 2015 Android browser comparison, Spanish software news and reviews site Softonic.com awarded Firefox version 37.0.1 the Best of 2015 nod, with reviewer Fabrizio Benedetti citing a good design, efficient memory consumption, the browser's open source nature, and independence.

[citation needed] As of early 2015, Google has stopped issuing its own patches for Android 4.3 and earlier to the WebView browser component and the WebKit rendering engine therein, which are used by the native/stock and often default AOSP browser in a large number of Android devices – thereby shifting the patching responsibility to device manufacturers.

[citation needed] This in effect extends the useful lifetime of devices stuck on older major versions of Android.

[79] On 30 June 2015, The Guardian Project announced a stable alpha of Orfox, the new mobile counterpart of the Tor Browser.

[80] The project removed in Orfox the WebRTC component and Chromecast connectivity, and app permissions to access the camera, microphone, contacts (address book), location data (GPS et al.), and NFC.