It records perfectly but there is no audio at all!

The extension does not support seekable WebMs. I think their web application supports this.

The tradeoff for the web application is that it only supports fullscreen recording.

Good so far. Not rating 5 yet because I have only done minimal testing.

The screen recording for a free extension of firefox addons is pretty good. I went with 5 stars until found out it does not capture audio so I changed it into 4 stars. Thanks anyway.