Firefox, Chromium on Debian: WebRTC H.264 is not supported

While trying to stream online with my friends, I had an issue where everyone else's computer can watch the stream but mine, and even my android device can watch it. I found [this test page from GitHub Mozilla](https://mozilla.github.io/webrtc-landing/pc_test_no_h264.html) that revealed I don't have H.264 support for WebRTC, while all my friends did. - I tested this on Firefox 112.0.1, both the Debian package firefox and the build from the official website. - I tested this on Chromium 112.0.5615.138 (Official Build) built on Debian 12.0, running on Debian 12.0 (64-bit) (provided by Debian package chromium). - I have installed libx264-160 and libx264-164. - I have installed libopenh264-7. Replacing it with competitor libopenh264-cisco7 makes no improvement. - I can watch H.264 encoded videos offline with MPV and VLC. - ffmpeg -codec lists h264 support: DEV.LS h264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 Nearly all documents and SE questions about H.264 support for Firefox are dated from around 2014-2017, which I infer this means this is an old, solved issue. If that's the case, why isn't Firefox detecting support for H.264? I use Debian Unstable (next release bookworm).