diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 123affe22..c108a1129 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -39,8 +39,6 @@ jobs:
         os: [ubuntu-latest]
         test-type: ${{fromJson(needs.test-type-matrix.outputs.test-type)}}
     env:
-      BROWSER_STACK_USERNAME: ${{secrets.BROWSER_STACK_USERNAME}}
-      BROWSER_STACK_ACCESS_KEY: ${{secrets.BROWSER_STACK_ACCESS_KEY}}
       CI_TEST_TYPE: ${{matrix.test-type}}
     runs-on: ${{matrix.os}}
     steps:
diff --git a/scripts/karma.conf.js b/scripts/karma.conf.js
index 81c2eec88..04072c830 100644
--- a/scripts/karma.conf.js
+++ b/scripts/karma.conf.js
@@ -7,10 +7,21 @@ module.exports = function(config) {
   // for options
   const options = {
     coverage: CI_TEST_TYPE === 'coverage' ? true : false,
-    preferHeadless: false,
     browsers(aboutToRun) {
       return aboutToRun.filter(function(launcherName) {
         return !(/(Safari|Chromium)/).test(launcherName);
+      }).map(function(launcherName) {
+        return launcherName === 'FirefoxHeadless' ? 'FirefoxHeadlessHighWorkerLimit' : launcherName;
+      });
+    },
+    customLaunchers(defaults) {
+      return Object.assign(defaults || {}, {
+        FirefoxHeadlessHighWorkerLimit: {
+          base: 'FirefoxHeadless',
+          prefs: {
+            'dom.workers.maxPerDomain': 10000
+          }
+        }
       });
     },
     files(defaults) {