It was great... but easily remedied without it Rated 5 out of 5 stars

I'll give this a 5 because when it did work it was just wonderful. Nice and light and did the trick, but the same is easily achieved if you edit your userChrome.css and add something similar to: html > body > img.decoded { background: none !important; }

This review is for a previous version of the add-on (initial.rev24.1). 

Thank you for the feedback. An updated and fixed version is on the way. If you want to download it early to try it now you can get it from https://addons.mozilla.org/firefox/downloads/file/235167/transparent_standalone_images-initial.rev28-fx.xpi?src=version-history, otherwise the add-on will update automatically when it passes add-on review.