ci: 🎡 reduce test duration in CI

addons/rose/testem.js

@@ -3,7 +3,7 @@
 module.exports = {
   test_page: 'tests/index.html?hidepassed',
   disable_watching: true,
-  launch_in_ci: ['Chrome', 'Firefox'],
+  launch_in_ci: ['Chrome'],
   launch_in_dev: ['Chrome', 'Firefox'],
   browser_start_timeout: 120,
   browser_args: {