Oh you can easily figure out render performance differences in milliseconds with your eyes. Try that. For example, a difference of 300 milliseconds is noticeable by me. I don't know what are you 'attesting' there. I'm not a web-developer, but just 'a developer'.

Also, what evidence you have that says Firefox can't be slow(even with all the add-ons it supports). In fact, those hundreds of bugs will be quite a sufficient evidence that it indeed is for many people. (It's coming from someone who still hasn't converted to Chrome)