> This approach is known to work - it's similar to the approach used by operating system kernels.
Unfortunately, this approach is also known to have several big problems. Take a quick spin through google for the "confused deputy" problem and you will see one of the primary complaints of ACL-based security. Capability-security researchers think they have a solution and in fact created a capability-secure browser called CapDesk several years ago. If anyone is actually interested in the problem they should check it out.