Bug 1919750 - Don't send SETTINGS_TYPE_MAX_CONCURRENT when push is disabled a=dmeehan

Original Revision: https://phabricator.services.mozilla.com/D222778

Differential Revision: https://phabricator.services.mozilla.com/D230530

modules/libpref/init/StaticPrefList.yaml

@@ -13262,6 +13262,14 @@
   value: false
   mirror: always
 
+# When true, Firefox will send a SETTINGS_MAX_CONCURRENT_STREAMS
+# parameter when push is disabled. Chrome doesn't send this,
+# so some servers misbehave when we do. See Bug 1919750.
+- name: network.http.http2.send-push-max-concurrent-frame
+  type: RelaxedAtomicBool
+  value: false
+  mirror: always
+
 - name: network.http.http2.push-allowance
   type: RelaxedAtomicInt32
   value: 131072  # 128KB

netwerk/protocol/http/Http2Session.cpp

@@ -1035,11 +1035,13 @@ void Http2Session::SendHello() {
     // The value portion of the setting pair is already initialized to 0
     numberOfEntries++;
 
+    if (StaticPrefs::network_http_http2_send_push_max_concurrent_frame()) {
       NetworkEndian::writeUint16(
           packet + kFrameHeaderBytes + (6 * numberOfEntries),
           SETTINGS_TYPE_MAX_CONCURRENT);
       // The value portion of the setting pair is already initialized to 0
       numberOfEntries++;
+    }
 
     mWaitingForSettingsAck = true;
   }