We recently removed IE mode from the Edge browser for Web Viewer and some users experienced issues where AFP type reports won't open outside of IE mode even though they have the AFP Plugin installed on their machines.
Note: Users were having issues in Chrome as well even though IE mode was never integrated in Chrome.
The Web Viewer application is working as designed in that Chrome and Edge do not support instantiating other applications or plugins while streaming the AFP Report data into the browser (AKA - they do not support the use of modal dialogs). That's why they default to saving the AFP report - because it must reside outside of the browser before it can be opened.
In-application rendering can no longer be done by any application; except for reports transformed to PDF files.