User Agent: Mozilla/5.0 (Windows NT 6.0; WOW64; rv:23.0) Gecko/20130428 Firefox/23.0 Build ID: 20130428031010 Steps to reproduce: That's not a bug but a question. We see some references to it in #504978 and #503175, but without giving details about the purpose, and that's not something specific to Mozilla. What is the use of these response header fields? (which apparently return the uncompressed length)
that's an http intermediary messing with your data. they sometimes update fields but rename the old version of them to something like that for debugging.