There could be more than one way to do this, but I found this easy to do. This method helps you to set specific persmissions like whether a specific site can load image or not, can open pop up window or not, can set cookies or not and can install extensions and themes or not. To do this, go to the webpage you want the permission to be set. Click on Tools - Page info. Then click on Permission icon. This shows you the above mentioned options. Most of those will have Use default checked unless you have changed it before. If you want to change permission, uncheck Use Default and select Allow or Block (See picture). I tried this in Firefox 3.x. I think it must be the same in Firefox 2.x, but I’m not sure.