Nice catch. It looks like our Channel feature is pulling the non-https image to display in the feed. Can you try editing the following file:
/components/com_jfbconnect/libraries/provider/twitter/channel/stream.php
Around line 80, you'll see:
$post->thumbPicture = (isset($tweet->entities->media[0]) ? $tweet->entities->media[0]->media_url : "");
to:
$post->thumbPicture = (isset($tweet->entities->media[0]) ? $tweet->entities->media[0]->media_url_https : "");
After you do that, clear the Joomla cache and test again. It may take an hour or so for all the old images to be updated though.
Please test and let us know how that goes!
Thanks,
Alex