@marksal,
Note that to set the Homepage, go to Settings --> Appearance and toggle the Show home button option “on”. Then, enter the custom address you’d like your homepage to go to – in this case, duckduckgo.com. Now, unless you want the home button displayed on your browser, you can toggle the Show home button to “off”, scroll down to New Tab Page shows and then select Homepage.
Now, any time you open a new tab, it will open with DDG.