The Firefox address bar can be used to type in keywords to query a search engine directly (see here). By default, the search engine used is Google. This can be changed to any search engine already installed in Firefox (see here). If you have fallen in love with the simplicity and security of searching using DuckDuckGo, then using it right from the address bar is worth the effort.
As of this writing, the DuckDuckGo search engine does not come pre-installed with Google. So, to be able to search from the address bar using DuckDuckGo requires 2 simple steps:
- Install the DuckDuckGo search engine into Firefox. There are a few variants of the search engine available here. I like to use the HTTP SSL version.
- Follow the same steps as for setting the default search engine (see here). The name string of this search engine (as of this writing) is
DuckDuckGo, so type this in as the value forbrowser.search.defaultenginename
That is it, type in keywords in the address bar and let DuckDuckGo deliver the results for you! 
Tried with: Firefox 9.0.1
