Firebase Remote Config on Web Now Tracks Rollout Changes Live

Firebase’s web SDK shipped a fix on July 9 that closes a quiet gap in Remote Config: the realtime onConfigUpdate listener wasn’t always firing when a rollout changed, if the rollout change didn’t also change a parameter’s visible value. firebase@12.16.0 bundles @firebase/remote-config@0.9.0, whose changelog entry reads simply: “Support realtime for Remote Config rollouts.”

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What was actually broken

Remote Config rollouts let a team ship a parameter to a percentage of users and expand it gradually, the mechanism behind staged feature releases and web A/B tests. Web’s realtime Remote Config, introduced in 2023, pushes onConfigUpdate events to connected clients the moment a template changes, instead of waiting for the next poll.

The problem: that realtime comparison was keyed to parameter values. A rollout can change which variant a given user is bucketed into, or shift which parameter keys it affects, without changing the value a client already holds. The old RealtimeHandler logic had nothing to detect that kind of change, so the listener could stay silent through a live rollout update. Android and iOS didn’t have this gap — their SDKs already compared rollout metadata, not just values.

Pull request #10106, merged June 25, adds a FirebaseRolloutMetadata interface (rolloutId, variantId, affectedParameterKeys) to the SDK’s fetch response, and rewrites RealtimeHandler to deep-compare rollout state on every update, not just parameter values. The PR description frames it as bringing the web SDK to “functional parity” with Android and iOS.

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Why it matters

If your app relies on onConfigUpdate to react to Remote Config changes instantly (swapping a feature flag, adjusting a UI variant), you were trusting an event that could silently skip a rollout-only change. Before this release, the workaround was polling: calling fetchAndActivate() on an interval instead of leaning on the realtime connection, which defeats the point of using it. That gap wasn’t documented as a known limitation; it just wasn’t handled by comparison logic that only looked at values.

Key Takeaways

• firebase@12.16.0 and @firebase/remote-config@0.9.0, released July 9, add rollout-aware comparisons to the web SDK’s realtime onConfigUpdate listener.
• Before this release, a rollout change that didn’t alter a parameter’s value could go undetected by realtime listeners on web, even though Android and iOS already caught it.
• The fix ships as FirebaseRolloutMetadata (rollout ID, variant ID, affected parameter keys) added to fetch responses, per PR #10106.
• No API changes are required to benefit — existing onConfigUpdate listeners pick up rollout-only changes automatically once you’re on 12.16.0 or later.

What to do

Update to firebase@12.16.0 or later if you use realtime Remote Config on web and run rollouts. If you built a polling workaround to catch rollout changes your realtime listener was missing, it’s now safe to drop — the listener catches those changes on its own. There’s nothing to opt into; the fix lives entirely in the SDK’s internal comparison logic.