A great extension for Firefox to capture website, it's called: Talon (Screen Capture & Aviary.com)

This addon for quick screen capture is a must-have for bloggers and designers alike! It will perform a screen capture and then open the image INSTANTLY in a basic image editor where you can do markup (draw arrows and rectangles), edit (crop, rotate and resize) and get the exact pixel colors of the image. A perfect companion tool for designers and bloggers!

Features include:

* Full or partial screen capture of all webpages and images (even Flash, in FF3.5+).
* Save to desktop, host online, or edit in 5 Aviary apps.
* Quick launch 4 Aviary design tools: Image editor, markup editor, vector editor, color palette editor & effects editor.

How to install this extension:

Go to https://addons.mozilla.org/en-US/firefox/addon/11587

How to use?

For a complete list of applications available go to http://aviary.com/tools