CefWithSyphon if a browser on mac capable of sharing screens between browser and cyphon (cyphon is mac equivalent of spout), is there a windows browser that supports spout?
Not currently that I am aware of. Some time back there were some experiments with Awesomium, but it is very old now. Screen capture might be one solution and you could have a look at what Newtek NDI can do with the latest tools they provide. Maybe this old post might give you a lead.
NDI have only screen captures from apps which are foreground on the screen (classic screen cap to video input model), i believe the CefWithSyphon example would allow for an app (example a browser built with CEF, open source Chromium) to be running in the background. This is especially cool, as a plugin can be designed for Resolume to input a URL and feed the websites content through sprout directly into resolume, all on the same box running resolume.
CefWithSyphon sounds very useful. Foreground screen capture is very fast if you can manage it and there is a Spout capture utility. But it might not be very convenient in practice. I think the older NDI tools had individual window capture but I am not sure where to find them. You might get a lead from a search of the NDI forum.