Same issue in Chrome and other browsers? Maybe https://stackoverflow.com/questions/2758608/window-focus-not-working-in-google-chrome will help. Hard to say without a JS demo showing the problem.

Can you redefine html dom methods in Opera? So that the redef only is valid for the target document? win.document.hasFocus = function(){ return true; }; Would that work?

@leocg Yes, it seems it does.