Index: test_runner.js
===================================================================
--- a/test_runner.js
+++ b/test_runner.js
@@ -42,17 +42,17 @@
 };
 
 function configureRunners()
 {
   let runners = "BROWSER_TEST_RUNNERS" in process.env ?
       process.env.BROWSER_TEST_RUNNERS.split(",") : [];
 
   if (runners.length == 0)
-    return ["chromium_remote", "firefox"];
+    return ["chromium_remote"];
 
   return runners.filter(runner => runnerDefinitions.hasOwnProperty(runner));
 }
 
 let runnerProcesses = configureRunners();
 
 function addTestPaths(testPaths, recurse)
 {