The browser is the most used outward facing software you will use. It interacts with suspect web sites and other internet sites. Firefox is still my first choice for security and plug-ins, even though Chrome offers a speed advantage that adds-up over the course of many hours of research, while this little problem makes me avoid MS Internet Explorer: Microsoft warns of critical IE9, IE10 zero-day-Just visit the wrong web site and get remote-code execution.
In Firefox, go to Tools>Add-ons>Plugins and set the Java Script and Toolkit to Ask to Activate. I also set all the other plugins to Ask to Activate as well. This prevents a plugin from activating at the wrong time and thereby sending out data to the site that caused it to activate. A malicious site may activate a plugin to have it to transmit data that can be used to thwart your investigation.
Third party cookies compile a long-term record of your browsing history. This is dangerous as it can reveal what you are investigating. In Options>Privacy>History select Never for third party cookies. In my sandbox, I have several versions of the browser with different settings. For example, I prefer to never accept cookies of any kind, but some sites need them to function so I have a version with normal cookies enabled.