Sergey Twersky Firefox actually is safe due to a known bug that stop's FavIcons from being saved and remembered. Thus , Firefox has to download the data fresh every time and report to the server its a new connection. In comparison to how it would normally work where the FavIcon incorporates the times the user has connected and the means they did that.
It's concerning how many ways these companies have at gathering intel on people and their usage without their permission. Even, if you block cookies, the favicon process apparently stores the data is a completely separate place that isnt cleared when users select Cache , Temp Folders etc.
I have a feeling this will be a hot topic and hopefully be addressed by those services who believe in privacy.