Office Add-in Javascript disabled?

Background

We have an Office Addin running in production and we've stumbled across a case with a customer where I suspect that his Mac computer won't run Javascript in Outlook. I haven't been able to confirm it but the symptoms point to that. For example, event handlers for buttons won't fire.

Questions

1. What browser is running the add-ins inside Office for Mac?
2. How can I confirm or deny that Javascript is running in Office?

I'm not sure what is going on here but if the add-in properly launches then we can rule out JavaScript itself not running. Were this the case the Office.initialize event would fire and Outlook wouldn't report an error.

As to what is actually happening, I would need a bit more information. They primary questions I have would be:

• Are they able to run other add-ins properly?
• Are they using Outlook 2016 against a modern Exchange Server or O365?
• Have the updated Outlook to ensure they have the latest bits installed?