Have you ever noticed the small site identification icon left to the address in the Location bar. It is one of the new features of Firefox 3 from where you can quickly have a comprehensive overview of the details of site. Click on it and it shows the site identity information. Now click on 'More Information' button and a window pop ups that contains comprehensive information about the details of the site.
General: This tab shows the general details of the website like type, Size of the webpage etc..
Media: In this tab one can see the list of all the media(image,flash etc..) objects present on the webpage. Here you can also preview the images and even save a whole gallery of images to your computer by using Ctrl+A and selecting the range of images and using the 'Save As' button.
Feeds: Here you can get the list of feeds provided by the website
Permissions: Here you can view and edit the permissions that particular website. Here you can disable the Cookies for the website or disable pop ups/image loads from the website.
Security: Finally here you will find the security details about the website like saved passwords, cookies etc.., and the encryption details of the connection.