When I run RESTIC_REPOSITORY=s3:s3.us-east-005.backblazeb2.com/... open -a Restic-Browser on Mac OS, restic-browser gets confused by the URL. It considers s3: to be part of the URL and fails to open it. See the screenshot (I used a fake URL for the screenshot, but a real one results in the same thing):

Fortunately, this is reasonably quick to fix if I click the "Open Repository" button and fix the URL each time.