When integrating a completely new feature, for example into Firefox Preview, this feature may only work with the latest version of an engine, e.g. the latest version of browser-engine-gecko-nightly. Manually maintaining a feature flag that gradually gets enabled in build variants as the required functionality becomes available in more stable engine versions (browser-engine-gecko-beta, browser-engine-gecko) is cumbersome, error-prone and potentially a multi-week long process.

To help build feature flags, that need to incorporate the engine version, every Engine exposes a version property. This property is an instance of EngineVersion, which makes it easy to match against specific engine versions.


Let’s say you are adding a new feature to Firefox Preview. This new feature requires brand new functionality that was just introduced in GeckoView Nightly 77.0. Using isAtLeast() you can create a feature flag that will enable this feature in all build variants that are using GeckoView 77.0 or higher.

// Enable feature with GeckoView 77+
val useNewFeature = components.engine.version.isAtLeast(77)

This also works for minor and patch versions as well as additional metadata that is appended to the version number.

// Feature requires GeckoView 77.2 or higher.
val useNewFeature = components.engine.version.isAtLeast(77, 2)

If needed you can access the individual parts of the version number manually:

// For GeckoView (Nightly) 77.0a1
engine.version.major // 77
engine.version.minor // 0
engine.version.patch // 0
engine.version.metadata // a1

GeckoView vs. WebView

Note that for GeckoView versions we are using the MOZILLA_VERSION that GeckoView exposes (e.g. 78.0a1) which can be different from version of the maven dependency (e.g. 78.0.20200528032513).

In browser-engine-system, which is using WebView, we are parsing the Chrome version from the User-Agent.

// Mozilla/5.0 (Linux; Android 10) Build/RPP2.200227.014.A1; wv)
// AppleWebKit/537.36 (KHTML, like Gecko) Version 4.0
// Chrome/82.0.4062.3 Mobile Safari/537.36

// On a device with a WebView with the User-Agent above:
engine.version.major // 82
engine.version.minor // 0
engine.version.patch // 4062
engine.version.metadata // .3