We don't have a way to prevent the jfbconnect.css file from being shown inline in the body of the page yet. We're working toward improved inclusions of our assets, and this is one task we have planned for the 6.2 release, this summer.
In the meantime, you can try the following minor code change which will prevent the CSS from being shown in the body. Depending on your settings, the file may be included in the head already and/or the CSS may not even be required for your display. Testing this may work for you to prevent it from loading and get you going until we have the final solution implemented later this summer.
To make the change, edit the /components/com_jfbconnect/libraries/provider.php file. Around line 189, you'll see:
$newText = '<link rel="stylesheet" href="' . JUri::root(true) . '/components/com_jfbconnect/assets/jfbconnect.css" type="text/css" />';
Edit that to:
$newText = '<link rel="stylesheet" href="' . JUri::root(true) . '/components/com_jfbconnect/assets/jfbconnect.css" type="text/css" />';
$newText = '';
I hope that helps, but if you need more help or have any other feedback, let us know.
Finally, just so you know, a small inclusion of a CSS file inline would cause an almost immeasurable delay in the loading of the page. Most browsers nowadays will load CSS files in parallel instead of 'blocking' as they used to. While it is best to have all CSS in the head, in the body really doesn't make a huge difference.
Thanks,
Alex