Force Outlook Add-in popup to open with embedded browser
Solution 1:
You should check to see if the displayDialogAsync API exists. It was added in requirement set 1.4.
If it exists, we recommend using it. Please note that the dialog can only call the Office.context.ui.messageParent API. This API allows the dialog to communicate one-way with the add-in. The add-in can use those messages to leverage the Office.js APIs.
If the displayDialogAsync API doesn’t exist you can leverage window.open. However, in this case the default browser will not be launched.