There is a known issue if you use Firefox 63+ to Record/Spy or for execution. When you select Firefox 63+, the following error dialog will be displayed and hence Firefox can’t be started:
Replace the current Firefox driver with the latest version (0.23.0)
- Select and download the appropriate type based on your current OS:https://github.com/mozilla/geckodriver/releases/tag/v0.23.0
- Follow this guide to replace the Firefox driver.
UPDATED: This issue is fixed on Katalon Studio 5.8.4, please download and use that version to resolve this issue.
Thanks for your understanding.