It only streams money when the tab is in the foreground and active. But yes, if you are on a monetized tab, get called for lunch, and don't lock your computer (what's wrong with these people , it could be that you stream all your funds to that one tab. I think the extension and the final browser UI once it's natively supported needs a way to let you limit the maximum amount of money, and also show you stats about where your money went so you can more easily adjust each site's amount.
