🐛 Fix firefox integration tests

[sergiomartins8]

• This is a small change
• This change has been discussed in issue 🐛 Fix firefox integration tests #19 and the solution has been agreed upon with maintainers.

---

Description:

1. Fix firefox integration tests as well as add them to the pipeline
2. Improve mock server initialisation logic
   • Instead of creating the mock server instance before starting the suit, it is now created when the listener calls for the getMockServerClient(). This introduces a better performance approach - initialisation is done only when/if needed.