To render pages on a throwaway computer and send only bitmaps, connect to the throwaway computer via VNC and run an ordinary browser.

As for improving on tab isolation over what existing browser sandboxes already offer, lightweight virtualization a la Firecracker seems like a more useful increment than containerization, and, assuming each tab has a similar VNC-like connection to its browser VM, virtualization would also make the whole "throwaway computer" setup less necessary to provide a meaningful security improvement.