Backed out 3 changesets (bug 1871963) for causing dt failures on browser_net_copy_as_powershell.js. CLOSED TREE

Backed out changeset 94e286542c9d (bug 1871963)
Backed out changeset dc2ad0369b86 (bug 1871963)
Backed out changeset 9fb8ccb2f305 (bug 1871963)

netwerk/protocol/http/HttpBaseChannel.cpp

@@ -1539,8 +1539,6 @@ HttpBaseChannel::DoApplyContentConversions(nsIStreamListener* aNextListener,
           mode = 2;
         } else if (from.EqualsLiteral("br")) {
           mode = 3;
-        } else if (from.EqualsLiteral("zstd")) {
-          mode = 4;
         }
         Telemetry::Accumulate(Telemetry::HTTP_CONTENT_ENCODING, mode);
       }
@@ -1645,14 +1643,6 @@ HttpBaseChannel::nsContentEncodings::GetNext(nsACString& aNextEncoding) {
     }
   }
 
-  if (!haveType) {
-    encoding.BeginReading(start);
-    if (CaseInsensitiveFindInReadable("zstd"_ns, start, end)) {
-      aNextEncoding.AssignLiteral(APPLICATION_ZSTD);
-      haveType = true;
-    }
-  }
-
   // Prepare to fetch the next encoding
   mCurEnd = mCurStart;
   mReady = false;