Re: Expires header vs Vary header

    From: Alex Rousskov <rousskov@measurement-factory.com>
    
    I am not aware of such dependencies. I would have guessed that
    Mozilla does not update Expires header when receiving a 304
    response, but then it would probably not have worked without the
    Vary either.

If Mozilla is not updating the Expires header when it receives
a 304 response with a new value for that header (as in the
example in Julian Reschke's message), then it is violating
this MUST:

   If a cache uses a received 304 response to update a cache entry, the
   cache MUST update the entry to reflect any new field values given in
   the response.

in RFC2616 section 10.3.5 304 (Not Modified).  This is restated
in more detail in section 13.5.3.

-Jeff