diff --git a/modules/libpref/init/StaticPrefList.yaml b/modules/libpref/init/StaticPrefList.yaml
index b8db30133e7a..1499edf4ab07 100644
--- a/modules/libpref/init/StaticPrefList.yaml
+++ b/modules/libpref/init/StaticPrefList.yaml
@@ -13199,9 +13199,10 @@
 # This pref controls whether to send the
 # SETTINGS_NO_RFC7540_PRIORITIES when stream dependencies
 # are disabled, and extensible prioritization scheme is in use.
+# defaults to false as some servers panic when they see this (bug 1928600)
 - name: network.http.http2.send_NO_RFC7540_PRI
   type: RelaxedAtomicBool
-  value: true
+  value: false
   mirror: always
 
 # This pref controls whether to send PRIORITY_UPDATE