Squid does not do (by default) any prefetching on its own. FireFox does, especially on a Google search result page which always adds
rel="prefetch" on the first link returned (which IS really annoying for privacy, your browser will always visit the first page without you ever clicking on any link).
Anyway that does narrow a bit where the issue might be and I will have a closer look at the requests. You probably trigger on the
X-moz: prefetch HTTP header, and the error returned is either filtered or misunderstood by Squid (must be HTTP 1.1 or something similar).
Keep you posted.
EDIT: you only return a
HTTP/1.0 403 Forbidden (text/html) so this is the normal behavior, Squid will only cache the error page.
Quickest fix is to disable prefetching in FF altoghether, which is probably better anyway:
http://developer.mozilla.org/en/Link...prefetching.3f
And I will not explain the long fix because this is obviously not what we want