PirateBrowser is a bundle package of the Tor client (Vidalia), FireFox Portable browser (with foxyproxy addon) and some custom configs that allows you to circumvent censorship that certain countries such as Iran, North Korea, United Kingdom,
The Netherlands, Belgium, Finland, Denmark, Italy and Ireland impose onto their citizens.
This is how it looks like:
No, it's not inteneded to be a TOR Browser, while it uses the Tor network, which is designed for anonymous surfing, this browser is ONLY intended to circumvent censorship.
The Tor network is used to help route around the censoring / blocking of websites your government doesn't want you to know about.
There have been no modifications to any of the packages used, no adware, trojans, toolbars, etc. This is simply a tool to help people get around censorship.