Firefox 44+ accepts a new kind of encoding (compression) called Brotli (br) for secure connections. Facebook has recently enabled Brotli (br) encoding for files send via a secure connections.

A possible workaround is to modify the involved pref and remove the trailing ", br" to prevent the server from sending files with Brotli compression.

• network.http.accept-encoding.secure = "gzip, deflate, br" => "gzip, deflate" (without quotes)

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

re: the-edmeister Firefox 44+ accepts a new kind of encoding (compression) called Brotli for secure connections and Facebook turned on Brotli encoding last night. Kaspersky doesn't know about this encoding and strips it from the HTTP response headers if you have "Inject script" checked in Kaspersky Settings -> Additional -> Network -> Traffic Processing https://forum.kaspersky.com/index.php?s=bbdfcf797a91bc90230472c52c4b103e&showtopic=351027