Add download button to Twitter image, and click to download the original image named by format.
As stated in the change log of v0.7, the feature you've mentioned was given up by the author of the script temporarily for the new Twitter UI, but you may wait for future updates.
download button in gallery mode has been added in version 0.8 ;)
Script updated today and now the button appears on the lower right of the enlarged image and works as did before. Thanks for the quick update!
New Twitter API's
After Twitter implemented the new API's the other day, the download button only shows on the timeline thumbnail and when you open the image, it is not there as it was previously. I noticed the extension has updated but this function was not showing and wanted to report. Thanks for your time and attention.