The WebPageTest team has now updated the test agent codebase and Firefox is working again.
Posted Aug 08, 2019 - 22:13 UTC
There are currently issues with synthetic testing using the Firefox browser. A change in Firefox is causing WebPageTest to error when trying to start a test. We're working with the WebPageTest team to identify and resolve the issue.
Posted Aug 08, 2019 - 11:13 UTC
This incident affected: Synthetic Data Collection.