Diễn đàn hỗ trợ Firefox

Whenever I play something in the browser while connected to my TV by HDMI, the sound still comes out of the laptop speakers. This happened suddenly, without any discernible reason, and I can't seem to fix it. Everything else works, only content played from Firefox remains in the laptop speakers. I've checked my audio mixer, nothing seems amiss, I've updated Firefox and refreshed the application, still nothing. Hell, I've even tried different cables and HDMI ports, but nothing works. What could be the issue? Why did my audio suddenly stop working, and what can I do about it?