Nice animation, very well placed.
When she freezes, you can try to deactivate the Add-On and activate it again. No big deal.

Great quality image, but sometimes she freezes (I think that's FF's issue though) and the text is pretty hard to read. My only complaint, really! The tab titles are pretty hard to read.

I love Derpy, but she freezes a lot. She'll start up again if you restart firefox thought