This addon won't be maintained further. I'm shelving this project due to lack of interest/utility and too much burden. The addon will remain available for download as long as the store allows, and the source on gitlab will also remain available to fork. I do have a greasyfork account you can check out, and you can get new versions of CSL, DID, and IBCP there! Available for Chrome too. Downloading images

(double)(right)click on images
hover over them and click the button that appears
drag and drop an image onto the hover button
select page content (or point at an image) and use the context menu

Extras

trigger a notification on successful downloads
rename downloaded images using patterns and variables for better mass organization*
use filters to limit functionality if it gets in the way
visually customize the hover button
"image downloaded" effect for visual feedback can be disabled

*uncertain support in Firefox: addon will automatically disable feature until supported FAQ

How does it work on thumbnail galleries? This addon downloads the image you directly interact with, i.e. the thumbnail. This is an unfortunately but deliberately omitted feature. Most browsers download link targets when alt-clicking on links, and most thumbnail galleries link each thumbnail to its full size source. Therefore, you do not actually need an addon to download most thumbnail galleries. For more complex galleries, addons dedicated to this purpose exist. You could also install Copy Selected Links and use a download manager.

The Options screen will automatically open after add-on updates if they force a change to any of your settings. Please rate/review/donate! :) A lot of time and work goes into creating my addons, and making changes or troubleshooting issues for users. This particular addon has cost hundreds of hours by now. Any donations are greatly appreciated. Cross-browser Please note that not all features work the same (or at all) as WebExtension support in browsers is not perfect yet. Problem, bug, broken, question, request? Per Mozilla policy, only an evaluation of an addon's entire function with reasonable expectations is a proper review. Vague complaints or 1-star ratings for single reasons are considered spam, as are false claims about the addon not working at all. For more detailed discussions, use the linked support site or email.