--- a/dom/plugins/base/nsNPAPIPlugin.cpp
+++ b/dom/plugins/base/nsNPAPIPlugin.cpp
@@ -2298,16 +2298,23 @@ NPError
           return NPERR_NO_ERROR;
         }
 
         rv = inst->WindowVolumeChanged(config.mVolume, config.mMuted);
         if (NS_WARN_IF(NS_FAILED(rv))) {
           return NPERR_NO_ERROR;
         }
 
+        // Since we only support for muting now, the implementation of suspend
+        // is equal to muting. Therefore, if we have already muted the plugin,
+        // then we don't need to call WindowSuspendChanged() again.
+        if (config.mMuted) {
+          return NPERR_NO_ERROR;
+        }
+
         rv = inst->WindowSuspendChanged(config.mSuspend);
         if (NS_WARN_IF(NS_FAILED(rv))) {
           return NPERR_NO_ERROR;
         }
       }
 
       return NPERR_NO_ERROR;
     }