@stemy Don't know about chrome-based browsers, but in Firefox add-ons can be enabled in private mode as well. Which I have enabled for Smart Referrer.
In Firefox, via about:profiles, you can create a new, fully clean, throw-away profile which you can use to test without any add-ons or custom configuration.
@RandySimons The default setting disables the addons in private mode, and check made, i didn't changed it.