Device Emulation — Viewport, Geolocation, User Agent

Foxbridge translates CDP Emulation domain methods to Juggler’s browser-level overrides. All emulation settings are scoped to the browser context, enabling per-agent device profiles.

Viewport

Emulation.setDeviceMetricsOverride sets the viewport dimensions:


CDP: Emulation.setDeviceMetricsOverride({width: 375, height: 812, deviceScaleFactor: 3, mobile: true})
  → Juggler: Browser.setDefaultViewport({width: 375, height: 812, deviceScaleFactor: 3, browserContextId: "ctx-abc"})

The mobile flag is not forwarded — Juggler does not have a separate mobile mode. Mobile behavior is achieved through viewport size, user agent, and touch emulation combined.

Emulation.clearDeviceMetricsOverride is a no-op.

User Agent

User agent can be set through two CDP paths. Both route to the same Juggler method:

CDP Method	Juggler Method
`Network.setUserAgentOverride`	`Browser.setUserAgentOverride`
`Emulation.setUserAgentOverride`	`Browser.setUserAgentOverride`


// Both of these produce the same Juggler call:
await page.setUserAgent('Mozilla/5.0 ...');
// or via CDP session:
await client.send('Emulation.setUserAgentOverride', { userAgent: '...' });

The browserContextId is automatically attached from the session.

Geolocation


CDP: Emulation.setGeolocationOverride({latitude: 37.7749, longitude: -122.4194, accuracy: 100})
  → Juggler: Browser.setGeolocationOverride({latitude: 37.7749, longitude: -122.4194, accuracy: 100, browserContextId: "ctx-abc"})

If accuracy is zero or negative, foxbridge sets it to 1 to avoid Juggler validation errors. All three fields are optional — omitting them clears the override.

Timezone


CDP: Emulation.setTimezoneOverride({timezoneId: "America/New_York"})
  → Juggler: Browser.setTimezoneOverride({timezoneId: "America/New_York", browserContextId: "ctx-abc"})

Locale


CDP: Emulation.setLocaleOverride({locale: "fr-FR"})
  → Juggler: Browser.setLocaleOverride({locale: "fr-FR", browserContextId: "ctx-abc"})

Media Type and Features

Emulation.setEmulatedMedia is sent to the page session (not the browser):


CDP: Emulation.setEmulatedMedia({media: "print", features: [{"name": "prefers-color-scheme", "value": "dark"}]})
  → Juggler: Page.setEmulatedMedia({type: "print", features: [{"name": "prefers-color-scheme", "value": "dark"}]})

Note that the CDP media field maps to Juggler’s type field.

Touch Emulation


CDP: Emulation.setTouchEmulationEnabled({enabled: true})
  → Juggler: Browser.setTouchOverride({enabled: true, browserContextId: "ctx-abc"})

JavaScript Enable/Disable

Emulation.setScriptExecutionDisabled does not have a direct Juggler equivalent. Foxbridge uses a Runtime.evaluate call to toggle the docShell.allowJavascript flag:


void(document.docShell && (document.docShell.allowJavascript = false))

This is a best-effort implementation — not all pages support docShell access. Foxbridge returns success regardless.

No-Op Methods

setScrollbarsHidden, setDefaultBackgroundColorOverride, and clearDeviceMetricsOverride return success without action — Juggler has no equivalents.

Context Isolation

All emulation overrides include browserContextId when available. This means different browser contexts (and thus different agents) can have completely different emulation profiles:


Agent A (ctx-1): viewport 1920x1080, timezone UTC, locale en-US
Agent B (ctx-2): viewport 375x812, timezone Asia/Tokyo, locale ja-JP

Both agents share the same Firefox process but see different emulated environments.