diff --git a/web-test-runner.config.js b/web-test-runner.config.js
index 3defb4bd5..a634f4371 100644
--- a/web-test-runner.config.js
+++ b/web-test-runner.config.js
@@ -66,7 +66,7 @@ if (env === 'firefox' || env === 'safari') {
   };
 
   config.files = tests;
-  config.concurrency = 3;
+  config.concurrency = env === 'firefox' ? 3 : 2;
   config.browsers = [
     sauceLabsLauncher({
       ...sharedCapabilities,