If you are using the Firefox browser on a macOS or Windows device and our user testing tool has trouble accessing your camera or microphone then this could be because you've disabled access to it in your browser settings.
When you're visiting the user test page check if in the address bar there is a camera/microphone icon. If there is click that and make sure your remove the "Blocked Temporarily" badges by clicking the cross icons. If there isn't an icon continue to step 2.
Copy and paste both links below in your Firefox address bar. Note those links will only work if you're currently using the Firefox browser.
Scroll to "Permissions" and click "Camera". Make sure nothing is blocked for "marvelapp.com" here. Close the modal/dialog and now do the same for "Microphone".
If you still are experiencing problems and you're using a macOS device it's worth to check out your system settings: Enable camera and microphone access on macOS