Audio has just stopped working on Macbook

In both Deshy Kernow and an Introduction to Cornish the audio tests have stopped working. I have checked tha my laptop is creating sound by testing with YouTube. I have seen this issue with Android and Chrome but I am using laptop and Firefox.

I have tried switching audio tests off then on again also muting and unmuting the sound in the settings and in the course themselves.

Any fixes or inspiration would be greatly appreciated.

Thank you.