RDP access

For the complete client and actor API, see the FirefoxRDP documentation.

Inspect tabs

The rdp fixture is the connected FirefoxRDP instance used by the harness:

const tabs = await rdp.root.listTabs()
const selected = tabs.find((tab) => tab.selected) ?? tabs[0]
if (!selected) throw new Error('Firefox has no open tab')

Obtain a target

Use the normal Firefox RDP actor hierarchy for operations not covered by the harness:

const target = await selected.getTarget()
const evaluation = await target.console().evaluateJS('document.title')
if (evaluation.hasException) throw new Error(String(evaluation.exceptionMessage))
console.log(evaluation.result)

The client also exposes generated actor fronts:

const watcher = await selected.getWatcher()
await watcher.api.watchTargets({ targetType: 'frame' })

Use rdp.front(actorId, typeName).api.method(...) for generated methods and rdp.actor(actorId).call(method, params) when a generic fallback is needed.

Firefox DevTools Local Mode

The harness localMappings option manages this watcher lifecycle automatically. For direct RDP use, Firefox 153+ requires the network resource watcher before its network parent actor is requested:

The package’s Firefox Local Mode compatibility patch adjusts these module imports in the browser/omni.ja archive so Firefox can load them from its distinct DevTools global. The package globalSetup applies this unified diff with the other Firefox patches.

const watcher = await selected.getWatcher()
await watcher.watchResources(['network-event'])
const networkParent = await watcher.api.getNetworkParentActor()
await networkParent.api.setLocalModeMappings({
  'app.localhost': '/absolute/path/to/app-fixtures'
})

Clear the mappings and stop watching when the page closes:

await networkParent.api.setLocalModeMappings({})
await watcher.unwatchResources(['network-event'])

Firefox Native Messaging

When nativeMessagingHosts is configured, the harness creates a private per-profile manifest directory and uses the chrome target’s privileged RDP evaluator to redirect XREUserNativeManifests through Services.dirsvc before it calls NativeManifests.init(). Firefox then caches the isolated lookup path for that instance. Linux uses the native-messaging-hosts subdirectory; fixture teardown closes Firefox and its native host processes before removing the temporary profile.

Firefox’s NativeMessaging.sys.mjs is hooked inside Firefox through privileged RDP evaluation. Only host names in nativeMessagingObservers are observed. The native manifest keeps the configured executable path; the harness does not check whether the binary exists or is executable.

Security

Firefox RDP is privileged, unauthenticated, and unencrypted at the TCP layer. The harness binds its endpoint to localhost. Do not expose the endpoint to a LAN or the public Internet.