Hello there, awesome plugin!
I`m using it on a project which needs to be validated on v3validator for html5. I found out that you have a HTML5 error in your widget:
All that needs to be done is just wrap widget code with UL tag and it passes validation.
Open font-resizer.php -> find # Generate the font-resizer text line and add echo with opening UL tag at the begining of the function and echo with closing UL tag at the end of the function.
Here`s a screenshot: http://prntscr.com/3bvp41