The installation is pretty straight forward and requires NO restart of your browser.
Simply click on the button that correspondents with your browser:
The download-button wil bring you to the actual download pages of the browsers.
In case of Firefox click on the "Download Now" button, in case of Chrome click on the "Add to Chrome" button.
When the installation is complete, you will see the NewsAssist 'toggle button' on the top right of the browser. (See #1 of the visual overview)