try setting ff version another way

scripts/karma.conf.js

@@ -27,6 +27,9 @@ module.exports = function(config) {
       if (CI_TEST_TYPE === 'coverage') {
         defaults = {};
       }
+      // pin Browserstack Firefox version to 64
+      // eslint-disable-next-line camelcase
+      defaults.bsFirefox.browser_version = '64.0';
 
       return defaults;
     },
@@ -36,9 +39,4 @@ module.exports = function(config) {
   };
 
   config = generate(config, options);
-  // eslint-disable-next-line no-console
-  console.log('config', config);
-  // pin Browserstack Firefox version to 64
-  // eslint-disable-next-line camelcase
-  config.customLaunchers.bsFirefox.browser_version = '64.0';
 };