Ubuntu Unity/Debian GNOME can auto-maximize Tor Browser
Ubuntu Unity automatically maximizes Tor Browser if the program tries to open its content window at a size equal to or greater than 75% of the total screen area. This includes occasions when the user clicks 'New Identity'. This exposes the user's real monitor dimensions to visited websites and third parties.
A workaround is to install and run compizconfig-settings-manager, navigate to 'Ubuntu Unity Plugin', then set the 'Automaximize Value' to 100%. After a restart, TBB behaves as it should: requesting a new identity, even after maximizing the window, causes the new window to open at a multiple of 200x100.