Greased LightMonkey is a GreaseMonkey script which helps us to enhance our image browsing experience. This works in all the websites which links to any image. This script will help you to view the full size of the image thumbnail links in the same page without having to navigate to any other browser tab or window .

This script comes with additional controls like slideshow, navigation, zoom options.

Keyboard shortcuts are available too…
| + |
Zoom In
|
| - |
Zoom Out |
| 0 |
Slideshow |
| x |
Close |
Note: GreaseMonkey needs to be installed in your firefox so as to make this script work. Install it from here
Tip:
- Close the lightbox containing the image by just clicking outside the image area.
- This script can be easily enabled or disabled by right clicking GreaseMonkey Icon in the status bar and check/uncheck Greased Lightbox from the menu.
Install Greased LightMonkey : 
After installation, go to the below links and click on the image thumbnails to popup the lightbox.
http://www.mozilla.org/projects/calendar/sunbird/screenshot.html
http://images.google.co.in/images?&q=31nst31n