Protect privacy on my Mac What is the best way to protect my privacy when using my Mac?

Assume I am a privacy-sensitive user, with Mountain Lion.  What software configuration should I do, to protect my privacy?  Is there any software you would recommend to protect my privacy, e.g., when using the web or other applications?  Which web browser is best, and what extensions are available to protect privacy while browsing the web?
What extensions are available to protect privacy while browsing the web?


I'm using Safari and there are a number of useful extensions for security.


Google SSL 

This extension makes it so every time you use the search bar, instead of searching www.google.com, your search is redirected to the Google SSL encrypted search site.
Do Not Track Plus

Do Not Track Plus blocks tracking technologies that advertisers and other companies use to track your browsing behavior. Easily see who is tracking you at each website you visit and block any or all of them.
Google Disconnect

Google is notified whenever you visit one of the more than 25 percent of sites on the web that include Google widgets (see http://j.mp/dcdefcon). Google Disconnect blocks traffic from third-party sites to Google servers but still lets you access Google services.
TrafficLight

TrafficLight is taking the security-while-browsing concept where it belongs: in the browser. This extension will add a strong layer of security over your browsing experience without inducing speed penalties or system resource consumption. Part of the processing is done in the cloud with some intelligent small engines that make various checks on pages you're visiting enabling you to have top notch antiphishing and antimalware protection.


You can check out some more security extensions here.

DuckDuckGo

Google is widely known to track and store personal data, so it's not a good search engine for maintaining anonymity and privacy. A good, secure alternative is the DuckDuckGo search engine. Here's a short comparison by AffiliatePrograms:


  
  DuckDuckGo strongly believes in privacy. Currently, the company does not record any user information. As you probably know, this is a sticking point with many people when it comes to Google. Company founder Gabriel Weinberg had this to say:
  “By default, DuckDuckGo does not collect or share personal information. That is our privacy policy in a nutshell.”
  It is often times described as a “hybrid” search engine thanks to results that are pulled from multiple sources including: Yahoo Search, Wolfram Alpha, Wikipedia, and its own crawler.
  


Incognito

Incognito is Safari web extension focused on Security. Here's a description from their site:


  When browsing the web, you are continuously being tracked. Not only by the websites you are visiting, but also by major companies that embed their 'content' into other websites through ads and analytics. As a result, companies like Google, Twitter and Facebook have an almost complete picture of your online activity.
  
  Incognito protects your privacy by blocking Google Adsense and Google Analytics on non-Google pages. In addition, it allows you to optionally block Facebook and Twitter content on third-party websites as well as embedded YouTube movies outside of the YouTube website.


Hope this helps!