Hello Richard,
You are welcome.
The thing is, CSS3 animations run smoothly on Webkit supported browsers (IE10, Chrome, Safari etc.)
Firefox, on the other hand uses Moz (by Mozilla itself) and even supports simple without prefix CSS3 rules, which does not turns out to be as smooth on lower end systems.
However, we had tried our best to make the animations as smooth as possible on all the browsers.
I'd recommend here to have the latest version on the Firefox, it seems to run smoothly on my lower-end laptop
Feel free to let me know if have any more queries.
Last but not the lease, please don't forget to rate the plugin on JED:
http://extensions.joomla.org/profile/extension/style-a-design/design/animate-it