Instead of general types like `Array` and `object`, use specific types
from the @types/chrome NPM package. This modifies only the JSDoc
comments, without any functional changes.

The filename may be used even if the user chooses “Open in browser as”.
I found two cases when this happens:
- The user chooses this option, but the browser can’t actually handle
  the given MIME type, and downloads the file anyway. (This can be used
  for example to force downloading XPIs or JARs as simple ZIP files.)
- The file is a PDF file. Firefox uses the filename when the file is
  subsequently saved from the PDF.js toolbar, as well as in the tab
  title.