Debugging this might be easier if you file an issue,
https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake-webext/-/issues

The check to see if WebRTC is enabled pretty straightforward,
https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake-webext/-/blob/main/util.js#L17

Is your `media.peerconnection.enabled` config set to `true`?