Not worked , re-installed Firefox then tried two methods, setting Firefox as the default browser in Windows but Opera as the preview browser in Construct 2, still opens Firefox, then I set Opera as the default browser in both Windows and Construct 2 but Firefox still opens.
Finally chose Opera as the preview browser in Construct 2 while it was the default in Windows, still opens Firefox.
Each time I made a change , I closed Construct 2 and re-opened it. Also applied a save to the project to see if that would make a difference and it has not.
Is there a registry or INI file that holds the setting ?