Why no (se)L4 microkernel/hypervisor based browser?

For example, Microsoft's Gazelle and Illinois Browser OS build their browsers based on a secure kernel, so why no (se)L4 microkernel/hypervisor based browser? I haven't even seen the idea. Besides, there is only old information about secure kernel/OS-based browsers in the first place, and nothing current and up-to-date. Perhaps it has failed?