I've read the comments on your site and I saw I wasn't the only one with this problem.
I tried to place
<?php jzzf_enqueue() ?>
Before and after the
<?php wp_head(); ?>
And I have the widget displaying, but the Formula is always "Invalid Formula" while it works if I place the form in a page.
PS: it would be good to update your FAQ to change "queue" by "enqueue"