Hi Matchbook, does the add-on menu item appear when you right-click on an image?

If not:

One possible reason is that it is a background image behind another element; currently, the extension does not detect those. Select Open Image in New Tab first and then right-click the image in the new tab (stand-alone image viewer). Another possible issue is not be enabled to run in private windows. More info on that in the following article: https://support.mozilla.org/kb/extensions-private-browsing

Next question: do the save buttons appear overlaid on the image after you select the right-click context menu item?

If not:

You can contact me for assistance using the Email link on the main page or the Issues tab on Github (add-on Homepage link).