Bug 1090087 - Add test for saving an image from a webpage

http://jenkins1.qa.scl3.mozilla.com/view/UI/job/flame-kk.ui.adhoc/253/console
Changed to local file used so that we don't add extra resources.
I could not get the test to work using cell data and the local file, so for now I will leave the external resource until bug 1084306 is fixed.