- Using dconf-editor edit: org > gnome > Epiphany > keyword-search-url; OR
- From the command line use this one-liner: GSETTINGS_BACKEND=dconf gsettings set org.gnome.Epiphany keyword-search-url https://duckduckgo.com/?q=%s.
For older versions:
- Go to > Menu > System Tools > Configuration Editor (or "gconf-editor" in the console).
- Drill down to key /apps/epiphany/general/url_search
- Overwrite the key with your ddg version of choice, e.g. https://duckduckgo.com/?q=%s for the SSL version (making sure to put the %s part at the end after the ' = ' symbol