Debugging in Microsoft Edge

I have long been able to successfully debug with sourcemaps in Chrome. We are seeing an issue specific to Microsoft Edge in our application so I would like to debug there. We are using GWT 2.8.0 and the Eclipse IDE.

(1) The application is compiled with safari in the user.agent; is that correct for Edge and relevant?

(2) I cannot get sourcemaps to load in Edge. I see this error in the Edge debugger (similar for all source files Edge is trying to load):

Could not locate http://localhost:9876/sourcemaps/ivo__admin/gen/com/google/gwt/aria/client/AutocompleteValue_FieldSerializer.java specified in source map http://localhost:9876/sourcemaps/ivo__admin/09F16AF198F7C1F3F9327E11B58EC86D_sourcemap.json.

And this error in the jetty console the log:

GET /sourcemaps/ivo__admin/gen/com/google/gwt/aria/client/AutocompleteValue_FieldSerializer.java

   Sent error page: unknown source file: gen/com/google/gwt/aria/client/AutocompleteValue_FieldSerializer.java

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