I've was able to shut it off in the past before it became submerged below the bottom of my screen but I'm not quick enough to nail it in pop up mode.
And I've never known where to find it or how to use it, even before it's submergence.
If there's anyway you guys could disable it or make it go away I'd be obliged.
I never want to see it again.
I don't have an easy way to do that yet. There is a button there so you can close the chat. But in your case you have part of your entire browser window hidden, probably by your task bar.
You really need to fix this for other reasons anyway. It's going to block other stuff you are doing.
Press the print screen button on your keyboard with your browser open
Go to your start menu and open up Mspaint
Go to the top love Ms paint refined paste
Now you have a screenshot of your computer and we can see what the heck is going on
You can Google on how to take a screenshot
The reason your chat is popping up sometimes it's because it's all hidden and someone is messaging you making it pop up but then it is getting hidden again.