The browser is where you should focus on first and foremost for internet
security. Advertisers, who are exceedingly savvy about this sort of
thing, know all too well that this is the primary place where you can be
discovered and targeted. Other interested parties are also aware of it.
For us the focus should be even more finely tuned in that the browser's
search engine is where we need to pay close attention.
Therefore, my preference among search engines is DuckDuckGo:
https://duckduckgo.com/
It has more than one Firefox plugin, depending on what all you want from
it. It has Community support, and it is growing more sophisticated. It
also has a strong "Do not track" policy, which you can find more about
here:
http://whatisdnt.com/
If you want to use it as the default provider in IE 9 or 10, this
options is available as well. Just take into account how much activity
you put into searching and understand the importance of it to your
anonymity. There is no such thing as a fool-proof solution, but you can
take steps in the right direction to help yourself substantially.