Legacy Runner sunset plan

Frequently Asked Questions

The Unified Runner replaces the legacy implementation for executing browser tests in the cloud, which is known as the Legacy Runner. Currently, mabl supports the following browsers on the Legacy Runner:

  • Firefox
  • Internet Explorer

By default, ad hoc and plan runs use the Unified Runner for Chrome.

Retiring the Legacy Runner

For a limited period of time, existing accounts can run tests against Firefox on both the Legacy and Unified Runners. We encourage all existing customers to migrate any plans that run tests on Firefox Legacy to the Unified Runner.



Trial users and customers who joined after February 15, 2023 do not have access to the Legacy Runner for Firefox.

When the transition period ends, the Legacy Runner will be formally retired.

Timeline for sunsetting Firefox Legacy

  • Extended support: February 15, 2023
  • End of support: July 3, 2023
  • End of life: October 2, 2023

Extended support

During the extended-support phase, the existing functionality of the Legacy Runner version will be maintained. However, new features may only be available on the Unified Runner. Bugs reported for the Legacy Runner will be addressed on a case-by-case basis.

End of support

No further changes will be made to the Legacy Runner version during the end-of-support phase. This includes non-critical security updates, non-security updates, and bug fixes.

End of life

During the end-of-life stage, the Legacy Runner version will be formally retired. All test executions will occur on the Unified Runner, where applicable.


Why is the Legacy Runner being retired?
The Unified Runner is the next generation of automated testing with mabl, providing a more reliable, consistent, and performant experience. The Legacy Runner will be retired as the Unified Runner was built to replace it.

Can I still use the Legacy Runner?
Yes, the Legacy Runner is still available for tests run on Firefox and Internet Explorer. However, there are some newer features we do not support in the Legacy Runner, including Intelligent Wait, accessibility testing, and shadow DOM support.

The Unified Runner

What improvements can I expect from the Unified Runner?
The Unified Runner is the next generation of the mabl testing service, bringing the same framework used in the mabl Desktop App and CLI to the cloud. By unifying our test execution logic, the new test runner provides consistent test results across all execution methods. This runner also offers considerable speed improvements.

Additionally, the Unified Runner introduces a new level of machine learning to mabl’s test automation platform: Intelligent Wait. With every run in the cloud, mabl collects timing information for each step to determine the expected wait before executing an action. This prevents test steps from executing before the application is in the correct state. These intelligent waits apply to test executions locally and in the cloud, allowing mabl to confidently test at the highest speed best suitable for the application under test.

Migrating to the Unified Runner

How can I migrate existing plans on the Legacy Runner to the Unified Runner?
You can learn more about how to migrate plans from the Legacy Runner to the Unified Runner here.

What happens if I don't migrate my tests to the Unified Runner by the sunset date?
If existing plans on the Legacy Runner are not manually migrated to the Unified Runner, they will automatically migrate to the Unified Runner on the date when the Legacy Runner is formally retired.

What areas of testing does this affect?
Switching browser tests to the Unified Runner only impacts runs in the cloud. Local test runs and Trainer replay already use the Unified Runner and will not change.

What should I look out for when migrating to the Unified Runner?
There are a few key things to note about the Unified Runner:

  • Internet Explorer is not supported.
  • Link crawler tests are unsupported at this time and will use the Legacy Runner.
  • Additional information on small behavioral differences can be found here.

What if I run into issues while migrating tests from the Legacy Runner to the Unified Runner?
Tests that ran successfully in the cloud on the Legacy Runner should continue to work in the Unified Runner. If something does not work as expected, please reach out to our support team with additional information.