[squid-users] ignoring If-Modified-Since: from browsers, but still generating If-Modified-Since: requests

We have a squid cache in accelerator mode which is working
nicely. When we implemented this we also implemented
conditional GET support (with If-Modified-Since:) in
performance-critical parts of our site, so that for
certain performance-critical requests squid could do a
fast internal conditional-GET and then serve the cached
copy of a resource.

This has had the side-effect of allowing browsers to make
If-Modified-Since: requests to the accelerator, which then
passes them through and possibly returns a 304 to the
client itself, rather than just internally.

Unfortunately, it turns out that If-Modified-Since:
support is broken in Mozilla when a Vary: header is
sent[1]. Therefore, though the site now works fine for
non-conditional requests, it behaves inconsistently for
the large part of the audience who have this broken
client. Therefore (and while we'd like to save the
bandwidth...) we need to have squid treat conditional GETs
as non-conditional; but obviously we still need to use
conditional GETs internally (otherwise we'd lose the
performance gain of using squid in the first place). Is
there a simple way to do this, or do I need to patch
squid?

 ---
 1. see https://bugzilla.mozilla.org/show_bug.cgi?id=269303

-- 
Don't look back. The lemmings might be gaining on you.