When Firefox on Windows 10 doesn't know how to open a file, Firefox will use a placeholder, "TWINUI," in the "Open with" drop-down. This typically happens after you've installed the OverDrive app (the app store version or desktop version), but haven't downloaded a title to it yet.

Note: Learn the differences between the Windows apps here, including what formats work with each app.

If you see this prompt:

  1. Click the drop-down menu, and choose the OverDrive app from the list.
  2. If you don't see the OverDrive app listed, choose Other... to find it.
  3. Click OK.
Last Updated: Sep 08, 2017 09:17AM EDT