WebExtensions is completely incompatible with most "Appearance" extensions (by design) and makes functionality enhancing ones like Print Edit practically start over from scratch to work around new restrictions. The few implementation options still available then get presented to users as "new" permissions that they must agree to. Never mind that the XUL version had MUCH more control over Firefox, yet nobody complained.

It makes sense that Print Edit WE makes a copy of the current page–so you don't have to refresh after saving or printing. The problem is that many sites get their content from AJAX and don't update the POST data correctly in PrintEdit's copy. This can probably be fixed if you are willing to share the details with the dev.

Frankly, I'm super impressed and amazed that DW-dev got Print Edit to work under WE at all. Extension developers like him tend to do this stuff in their spare time. The least you can do is bear with him during the transition.