For a Mac user, you don’t need to use any third-party applications to capture Safari screens, since which can be done by the Mac default capture tool.
But, if you are using Safari in a Windows system, or if you want more than just a screenshot, such as to upload it to a file hosting service and share it to Facebook, MySpace, Twitter or some other social networking sites, then you can check out the following best 2 screen capture extensions:
1. Awesome Screenshot
Awesome Screenshot is available for you to capture the visible part of page, then you can edit the screenshot, save it as a PNG file, or upload it to the Awesome Screenshot website and then share it on Facebook, Twitter, Google Buzz or send it via Gmail, Yahoo mail or Hotmail.
By the way, the Awesome Screenshot extension is also workable for Chrome and Firefox.
Snapper is also available for you to capture the visible part of page, you can’t edit the screenshot, nor share it directly, but you can drag it to your desktop.