It is really wonderful how, when this extension activates, it grays out the image for a second to let you know that it worked, and it also shows the file name on the right side to ensure that you've not accidentally saved the same picture twice. If it happens that two different pictures being saved have the same name on the website, it kindly automatically adds a number to the end of the file name so there is no hassle! It didn't work for me before I updated to Firefox 57, but that really was a matter of updating Firefox. 5 stars, thank you developer!