In Firefox, it is always easy to save images. All you have to do is right-click on an image, and select “Save Image As” option. But many time it happens that when you right-click on an image, this option does not appear. Even worse a small transparent image is saved like in case of Orkut profiles. Sauravjit had similar problem while saving a pic from fashion website.
This happens because, image you are viewing is set as background using a CSS trick. Technically you can just open source code and find image path without much trouble, but many people would like to make it simple.
Backgroundimage Saver is a simple firefox extension that provides help in such cases. When installed, it automatically detects such background images when you click on them and shows “Save Background Image As” option, as highlighted in screenshot below.
[Update: Added missing download link for firefox 3. Thanks to Mini’s comment.]