Your plugin breaks the "font uploader" plugin

as a matter of fact, when I set it to appear on scroll, my custom header fonts vanish to the default boring WP font the moment your bar becomes active

And to add onto that, it overrides Google Fonts plugin settings too by changing the font to the default one…

Thank you guys, we are working on it!
Fix will come with the next release.

You need some work around to fix this issue:
Update the following:
echo '<style type="text/css" media="screen">';
to
echo '<style type="text/css" media="all">';
in /wp-content/plugins/font-uploader/includes/styles.php
in line 5.