Comment 7 for bug 360713

udude: Nope, that's it, 2048 is your max, which means my external monitor is limited to 1024 if I want it left-of or right-of the internal screen. I only have an ancient 17" so it doesn't bother me, but I agree it doesn't seem reasonable.

I don't know if there are any plans to change this limitation... I'll dig through the wishlists and if I can't find this request in there, I'll post one. Might be a hardware limit though.