To download an image, use option+click then Save Image as...
With other browsers you can just drag the image to the desktop, but this doesn't work with Classilla - it saves the URL instead.
As for Google Images, it worked once upon a time. But then they changed something to make it worse.
Following the image links in Google does not work for me in Classilla. Work around is to delete the '
http://www.google.co.uk/imgres?imgurl=' bit from the URL.
Or just use another browser, which will be quicker too.
This is all assuming the source website plays nicely in the first place.