Dux-Soup can be installed using Chrome only. Just visit the Chrome Webstore and click "Add to Chrome".
However, if you are unable to download the Dux-Soup extension from the Chrome Web Store you install Dux-Soup manually following these steps.
First download the latest via https://download.dux-soup.com/latest/ , and select the most recent version from the list.
Then, to install:
1. In Chrome, Go to Settings - icon > More Tools > Extensions ( click the ‘...’ icon in the top-right corner )
2. Enable Developer Mode ( toggle button in top-right corner )
3. Drag and drop the ‘.crx’ extension file onto the Extensions page from step 1 ( crx file should likely be in your Downloads directory ), and select "Add extension"