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WebChannels in Fenix & WebExtensions

Current as of December 2nd, 2019

Communication with OAuth WebChannels

OAuth WebChannels is an extension of the FxA WebChannel Desktop Flow. It consists of similar messages as the Desktop Sync flow, however is more generic because of the use of OAuth in the background. Some behaviours in the OAuth flow are different.

This flow currently supports the following messages:

  • fxaccounts:fxa_status
  • fxaccounts:oauth_login

The fxaccounts:fxa_status message in the OAuth flow supports specifying a custom list of Sync engines that the app supports. See FxA WebChannel Desktop Flow for details of engine capabilities.

Communication with GeckoView applications

To enable this feature in applications with GeckoView we ship a WebExtension as part of the firefox-accounts Android component.

Communication channel is established from web content to this class via webextension, as follows:

sequenceDiagram participant fxa as FxA web content participant glue as glue - fxawebchannel.js participant webext as Web Extension fxa-->>glue: WebChannelMessageToChrome JS Event glue-->>webext: Port message webext-->>glue: Port message glue-->>fxa: WebChannelMessageToContent JS Event
sequenceDiagram participant fxa as FxA web content participant browser as Browser fxa-->>browser: fxa-status - request account status & device capabilities browser-->>fxa: response-based on state of [accountManager] fxa->>fxa: user authenticates/authorizes fxa-->>browser: oauth-login - send OAuth code, state, syncEngine info



See the fxaccounts:fxa_status section of the WebChannel Protocol document.

engines capability

Unlike the Desktop WebChannel integration, the OAuth WebChannel integration expects all supported engines to be enumerated within the engines capability. Possible values are:

  • addons
  • addresses
  • bookmarks
  • creditcards
  • history
  • passwords
  • preferences
  • tabs


Sent when a user successfully authenticates via a WebChannel OAuth flow.


"code": "02f3cfea84ac4c143662b38d6c7f0c82c6f91eb041befc7cecda446b1b4887c1",
"state": "vHao1p6OizzwReCkQMSpZA",
"redirect": "urn:ietf:wg:oauth:2.0:oob:oauth-redirect-webchannel",
"action": "signin",
"declinedSyncEngines": ["history"],
"offeredSyncEngines": ["history"]


Supported by oauth_webchannel_v1 context.

See also