This extension is based on jquery-letterfx.js by TuxSudo: http://tuxsudo.com/code/project/letterfx
This (free) extension is another one from my private collection.
More information
https://www.wysiwygwebbuilder.com/letterfx.html
You can download the new extension via the Extension Manager: Menu->Tools->Extension Manager->Online Gallery->Miscellaneous
Please read the included (PDF) document for help.