Monitor Audio Router Bridge by TechlyAccurate

Monitor Audio Router Bridge is the Firefox companion extension for Monitor Audio Router, a Windows tray app that routes app audio based on which monitor the app or browser window is on.

This extension helps the desktop app handle browser audio more accurately by sending local audible-window hints through Firefox native messaging.

Requires the Windows desktop app:
Download Monitor Audio Router

Source code and documentation:
GitHub repository

What it does
- Reports audible Firefox windows to the local Monitor Audio Router desktop app.
- Helps route browser audio to the playback device assigned to the monitor.
- Supports the desktop app's per-monitor routing configuration.
- Works through native messaging with the local companion app.

Privacy
- No telemetry.
- No remote server communication.
- Does not send browsing history, URLs, page contents, or analytics.
- Sends only local routing hints to the local native messaging host.

Those hints can include browser name, audible window bounds, browser window IDs, audible tab titles, and active tab title for matching.

Limitations
Modern browsers may share audio processes between multiple tabs. The extension improves browser-window routing, but it cannot always route multiple simultaneous audible tabs independently when Firefox reuses the same audio process.