In my picker options I have specified that I only want files with a certain mimetype, but files with that mimetype are still being rejected? What gives?

The Filestack modal uses an html input tag for selecting local files eg. <input type="file">.

When you set the mimetype or extension parameter in your picker options, it adds an 'accept attribute' to the tag. For example, for the application/octet-stream mimetype it adds: <input type="file" accept='application/octet-stream'> to the tag.

However, the mimetype can vary depending on what browser or operating system you are using. For example, PSD files have the mimetype application/x-photoshop in Firefox, but show up as image/vnd.adobe.photoshop in Chrome.

The best way to deal with this is to include both mimetypes in your mimteypes array.

filepicker.pick(
  {
    mimetypes: ['image/vnd.adobe.photoshop','application/x-photoshop']
  },
  function(Blob)
  {
    console.log(JSON.stringify(Blob));
  }
);