i wouldn't bother with add-ons the best solution is the manual way. add-ons might contain viruses, i don't personally know anything of the one you mention here, and all it is doing is something the browser already supports. i have personal experience of your problem, i like to keep a folder of sci-fi inspiration pics on my harddrive, and know it is bothersome but just get into that mechanical routine of:
1.right click on image
2."open link in new tab"
3. go to the new tab
5."save image as"
6.have the folder you want them to go to already prepared to be the first location opened by the file browser
7.leave the image name as is, it's too much bother to rename
or some more bothersome method for less pleasantly laid out sites and those that try to make it even harder to download pics.flickr can be particularly bad for this by making right clicking on the image display the right click menu for a link rather than a picture.
as a general rule don't trust programs to do things you could do yourself, and if it takes long enough for 10 beers how many pics are you downloading!
Back on this site, for a while anyway, been so busy the last year.
My systems:2 laptops, intel i3 processors, windows 8.1 installed on the hard-drive and linux mint 17.3 MATE installed to USB