Save images into specific folders with the following Addon for Firefox.
Organize your images easily into specific folders while you download them, saving a lot on your time and effort.You can Send them into your favorite folders with just a few clicks once you configure the addon without going through the time consuming default Save Image As folder structure, right from the contextual menu.
Double clicking on a Image in a web page would save the image in the folder that was last used by the addon without going through the contextual menu again.
You can even set it to overwrite a file with similar filename or increment the file name with a number and save it when there are files in that folder with a similar file name.
Link:Save Image in Folder 1.1.3