Container tabs for geckoview/android

[rnei]

I've been following the container requests for Android for a while now, and I want to add a technical point that I think gets overlooked in these threads.

Private Browsing and Containers already use the exact same underlying mechanism in Gecko. Both are just values on the same OriginAttributes struct, one is privateBrowsingId and the other is userContextId. They're not separate systems bolted together, they're the same partition key with a different number in it. This is documented in Mozilla's own source docs and confirmed in old Bugzilla threads, where engineers note directly that private browsing uses the same mechanism as containers.

Firefox for Android already runs Private Browsing successfully, which means it's already creating and managing an isolated storage jar (userContextId/privateBrowsingId = 1) separate from normal browsing (0). And since GeckoView runs on the same Gecko engine as desktop, and Fission (site isolation) is already enabled by default on Android as of Firefox 147, the core isolation architecture needed for containers appears to already exist under the hood.

What seems to be missing isn't engine level plumbing, it's the app layer in Fenix: a UI to create/name/color containers, a way to assign a tab to one, showing which container a tab belongs to in the tab tray, "always open this site in Container X," and exposing it through the WebExtensions API on mobile like the desktop containers extension does.

Given that this "hard" isolation problem already looks solved for free by other work already shipped on Android, could someone from the platform or Fenix team clarify what the actual remaining blocker is? Is it UI/UX design, extension API work, sync, or something else? A lot of us would find it easier to understand the wait if we knew what specifically is left, rather than "it's planned" with no further detail.

[Jon]

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