Browser extension to create independent cookie stores narrower than spec

Does anyone know of a browser extension (preferably Firefox) that allows you to create independent cookie stores at a finer (and configurable) granularity than the specification?

E.g. say http://a.example.com/ first sends

Set-Cookie: a=bar; expires=Fri, 31-Dec-2010 23:59:59 GMT; path=/; domain=.example.com

So clearly this would also be sent by Firefox for anything subsequently requested under http://b.example.com/ . I want the extension to not send the header for b.example.com. Typically, this will cause b.example.com to send a different set-cookie header, which would then be resent only for b.example.com. The idea is to create multiple independent sessions on the same site.

It would be an added bonus if it supported other granularity 开发者_如何学Pythonschemes (e.g. http://example.com/a/ is separate from http://example.com/b/).

This strikes me as somewhat similar to Applications Boundaries Enforcer, but different and not within its scope (though I could be wrong).

Finally, I'm aware that this could give you enough rope to hang yourself.

You can do something similar (multiple browser windows with different cookies and settings) with Chrome's multiple user feature.

This might be doable with Firefox profiles too, and -no-remote.