Would've be nice to make the browser capable to spread out in both monitors. For example, I designed a web app for my company and it's almost like a OS with different apps and all, most apps open in it's own windows. Let say you open a tab then click somewhere in the browser toolbar, extend browser to second screen, then a new slave tab is open and positioned in the next monitor. That way all draggable elements can be dragged from one screen to the other.
It's just a crazy idea I had today. If you select full screen then both tabs cover both screen, independently.