save image as not working

ive looked everywhere, here and all over the web. seems im the only one with this problem and im ready to kill my browser! sometimes when i go to save image as on firefox and save the pic, go to its location to view it the only thing there is a 'sliver' of the image like its been shrunk into a tiny thin line! when i go to choose which format to save it as(i.e jpg) the drop down box is empty and shows nothing when u try to pick a format. im missing out on some awesome pics i really need and want. pls someone help! ty!