A server MUST NOT send transfer-codings to an HTTP/1.0 client
In firefox the page renders as empty. If you view source you can see part of the page (i.e. the first chunk) was downloaded, but the full content has been truncated.
Moving squid to HTTP 1.1 should probably fix this, except according to squid.conf it won't:
# Enables HTTP/1.1 support to clients. The HTTP/1.1
# support is still incomplete with an internal HTTP/1.0
# hop, but should work with most clients. The main
# HTTP/1.1 features missing due to this is forwarding
# of requests using chunked transfer encoding (results
# in 411) and forwarding of 1xx responses (silently
So the solution is to drop the accept-encoding header for the microsoft.com domain:
acl support.microsoft.com dstdomain support.microsoft.com
header_access Accept-Encoding deny support.microsoft.com
OR if you are using IE, apparently you can untick "Use HTTP1.1 through proxy connections" in IE’s Advanced internet options tab.