your domain1.com site, and download from domain2.com? (in this case, YouTube?)
<a href="http://domain.com/file.txt" download>click</a>
Alas, a relative resource address is required for ff, or see CORS Headers FF
As an option - to make a separate controller method, make the link relative, but in the Beck, the request goes to the address you need, for example:
<a href="download?somefilename=file.txt" download>click</a> public FileResult Download(string fileName) { byte[] fileBytes = System.IO.File.ReadAllBytes(@"http://domain.com/file.txt"); return File(fileBytes, System.Net.Mime.MediaTypeNames.Application.Octet, fileName); }