--- a/testing/mochitest/runtests.py
+++ b/testing/mochitest/runtests.py
@@ -2716,18 +2716,19 @@ toolbar#nav-bar {
 
         def dumpScreenOnFail(self, message):
             if self.dump_screen_on_fail and 'expected' in message and message[
                     'status'] == 'FAIL':
                 self.harness.dumpScreen(self.utilityPath)
             return message
 
         def trackLSANLeaks(self, message):
-            if self.lsanLeaks and message['action'] == 'log':
-                self.lsanLeaks.log(message['message'])
+            if self.lsanLeaks and message['action'] in ('log', 'process_output'):
+                line = message['message'] if message['action'] == 'log' else message['data']
+                self.lsanLeaks.log(line)
             return message
 
         def trackShutdownLeaks(self, message):
             if self.shutdownLeaks:
                 self.shutdownLeaks.log(message)
             return message
 
     def getDirectories(self, options):