Thanks for getting back. Wrapping it in s.doPlugins is fixing the error, but I have some collateral effects, so I ended up running my plugin code (making use of document.body) in a rule instead of the custom extension editor. In addition, I conditioned the plugin code if document.body exists. This w...

Another one, slightly different:  

Thanks for asking. Here is the screenshot showing the error (this comes from https://www.genesis.com/ch, same website but different country):  

Thanks for helping out. You may see the error in Firefox console on https://www.genesis.com/uk