To do so:
1. Make sure you are using the Firefox Web Browser
2. Install the NoScript Add-on
3. For greatest ease-of-use, configure NoScript to:
A. Allow Scripts Globally, and
B. Disable Scripts from startpage-proxy.com and its subdomains.
Or, for protection even when you are not using the Startpage Proxy, with some inconvenience, configure NoScript to:
A. Block scripts globally, and
B. Enable Scripts from startpage.com, its subdomains, and any other trusted websites -- but not startpage-proxy.com.