Install Firefox
firefox uses google safebrowsing , so every time you fire up firefox it lets google know your ip of the day in return for updating its database of malicious websites , that is irrespective of what your search engine preferences are and such behaviour is enabled by default .there is no way to know what is being sent because it is encrypted. if you wish to test this out , use wireshark. this information can be used to log your behaviour through google+ widgets and like buttons as you hop through the internet.
Install Firefox add-ons
most firefox addons , including privacy addons have been known to connect to log their users and as such the behaviour of these addons can not be studied because contrary to the browser itself which is somewhat free , the addons source code is not supplied under any particular free license because the addons market does not require them to be.
From an email:
http://ashkansoltani.org/2012/02/25/cookies-from-nowhere/ https://mailman.stanford.edu/pipermail/liberationtech/2015-April/015236.html
solution : gnu icecat
https://mailman.stanford.edu/pipermail/liberationtech/2015-April/015236.html
solution : use only truly free addons , build when source code is available