Not Good. Rated 2 out of 5 stars

I don't see how to tell this add-on to reload a DIFFERENT icon for a given site if you don't like the BRIGHT YELLOW one it already generated for a site.
Great concept though.
You should allow us to recreate icons for a given site until we like one.

This review is for a previous version of the add-on (0.3.4.6). 

You can't. The shape and color of the icon is determined by an algorithm from the website's name, as explained in the add-on description. If you don't like the icon generated for a particular site, you can disable icon generation for that site in the preferences window of the add-on, and use another add-on (e.g. FavIcon Picker) to manually set a favicon for that site.