http://www.extremetech.com/computing/178587-firefox-is-still...
http://www.extremetech.com/computing/178587-firefox-is-still...
Most of the security issues we encounter are with bugs in the driver. A common bug for example with the Intel mac driver is when sending allocating a valid large texture the texture will sometimes instead be filled with old gpu memory[1]. Then you can glReadPixel the data and reconstruct parts of the desktop windows or tabs. A sandbox isn't going to stop you from exploiting this kind of buggy driver if it incorrectly starts returning other people's data when you asking for unrelated valid commands.
"... The [Servo] engine processes will use the operating system sandboxing facilities to restrict access to system resources."