--- a/netwerk/protocol/http/nsHttpHandler.cpp
+++ b/netwerk/protocol/http/nsHttpHandler.cpp
@@ -400,16 +400,21 @@ nsHttpHandler::IsAcceptableEncoding(cons
 
     // HTTP 1.1 allows servers to send x-gzip and x-compress instead
     // of gzip and compress, for example.  So, we'll always strip off
     // an "x-" prefix before matching the encoding to one we claim
     // to accept.
     if (!PL_strncasecmp(enc, "x-", 2))
         enc += 2;
 
+    // gzip and deflate are inherently acceptable in modern HTTP - always
+    // process them if a stream converter can also be found.
+    if (!PL_strcasecmp(enc, "gzip") || !PL_strcasecmp(enc, "deflate"))
+        return true;
+
     return nsHttp::FindToken(mAcceptEncodings.get(), enc, HTTP_LWS ",") != nullptr;
 }
 
 nsresult
 nsHttpHandler::GetStreamConverterService(nsIStreamConverterService **result)
 {
     if (!mStreamConvSvc) {
         nsresult rv;