Nested Tabs

I'm sure everyone loves having multiple tabs in one window, but how
about multiple tabs within a tab? I believe we would all find such a
feature to be of great utility to our web-browsing. For example, when
researching on a subject, I'm sure we tend to open way too many tabs
that can quickly get very disorganised. I believe that some form of
nested tabs should help alleviate the problem.

Hope I'm not suggesting something that has already been suggested by
someone else. Please give your thoughts on this. Thanks!