This is tough to implement when the feature is present, but implemented wrong

Sometimes it’s doable if you can call the API and check that the result is what you’d expect. For example, a long time ago some browsers incorrectly handled particular Unicode characters in JSON.parse. Sites could check for the incorrect behaviour and shim JSON.parse with a version that fixes the output.

I’ve never worked with WebRTC but I imagine it might be difficult to do that with some of its APIs given they require camera or microphone access (meaning you can’t check for the bug until the user actually tries to use it).