Hi Tate,
The Links contained within Method that open up the Report Designer are actually download links to install the program itself. The Blank Popup screen you are seeing is a download window, you should see a file called MethodReportDesigner.application being downloaded when the popup shows.
To edit your reports in the Report Designer, you have to open them up directly in the Report Designer Application. After opening the Report Designer, you will need to open the report you are trying to edit by navigating to File > Open and entering your Method Account credentials.
Thanks Tate!
Regards,
Ben