Monitor Black Out ?

[Washac]

When in Youtube and I choose to watch in full screen on either monitor the second monitor sort of slides to black, does the
same on Twitch, I'm pretty sure it never used to do this, but its not often I go full screen so may be wrong on that its only just started.

Browser used is Firefox.

 

[FreakinEurekan]

Could be the System Settings > Desktop & Dock > Displays have separate Spaces setting. If that's not enabled, you only get one full-screen app at a time regardless of how many displays you have.

 

[Washac]

Could be the System Settings > Desktop & Dock > Displays have separate Spaces setting. If that's not enabled, you only get one full-screen app at a time regardless of how many displays you have.

That was the answer. many thanks for that appreciated.