Use Firefox for system specs in GitHub Actions

In general, we can run system specs with four browser combinations:

1. Chrome
2. Chrome Headless
3. Firefox
4. Firefox Headless

Unfortunately, Selenium has an ongoing issue with Chrome Headless and Alerts, making the test execution slow or causing random failures. Non-headless Chrome works fine.

To overcome these issues, we switch to Firefox for the time being in GitHub Actions. Non-headless browsers are not supported in GitHub Actions.

Author: MrSerth

.github/workflows/ci.yml

@@ -78,6 +78,9 @@ jobs:
         env:
           RAILS_ENV: test
           CC_TEST_REPORTER_ID: true
+          # Use Firefox for system tests until Chrome headless works reliably again.
+          # See https://github.com/SeleniumHQ/selenium/issues/15273
+          BROWSER: firefox
         run: bundle exec rspec --color --format RSpec::Github::Formatter --format progress
 
       - name: Upload coverage reports to Codecov