I've found it incredibly difficult to download images from twitter, especially when there are more than one in a gallery. This script adds a download button beneath the image allowing you to quickly and easilly open the current image in a new tab.
For even faster downloading, ctrl-click or middle mouse click the button to open the image in a new tab and stay on the current page.
You will need a browser extension for loading userscripts. The reccommended ones are Greasemonkey for Firefox, and Tampermonkey for Chrome.
To install the userscript, simply click the link below, or go to the ".user.js" files in the repository and click the "Raw" button in the top right. Your userscript extension should recognize the script and ask if you would like to install it.