Why does my FF (android) use a different search engine when my query contains only one word?

I switched from chrome mobile to firefox in android after this whole NSA spying/prism thing in order to change the default search engine to duckduckgo instead of google. I did so in about:config by changing keyword.URL and browser.search.defaultengine. Now, when I type a single word into the address bar FF decides to use Norton SafeSearch. However, if my search query in the address bar contains 2 or more terms, the appropriate search engine is used (duckduckgo). How can I kill this annoying little Norton Safe Search thing? I have no addons or apps even installed in firefox, beyond the addons for duckduckgo. Beyond that, it is literally a fresh install.