Most of the issues with firefox, drupal, whatever are coming from plugins anyway.
Protocol based interactions (that requires clear API) do a better job at isolation than modules.
In a certain way linux too the obligation for drivers to be runned kernel space and thus the adaptation made for drivers to access resources have made some part of the kernel internal API klugish. On the other way, it is true that the use of modules without API enables linux to present an external API that does not change while you can modify the behaviour of the kernel and its internal.
(I guess there is a price to pay for everything, but not everybody is a genius like Torvalds)
Protocol based interactions (that requires clear API) do a better job at isolation than modules.
In a certain way linux too the obligation for drivers to be runned kernel space and thus the adaptation made for drivers to access resources have made some part of the kernel internal API klugish. On the other way, it is true that the use of modules without API enables linux to present an external API that does not change while you can modify the behaviour of the kernel and its internal.
(I guess there is a price to pay for everything, but not everybody is a genius like Torvalds)