DuckDuckGo Wikipedia v1.1
This search engine add-on will redirect directly to DuckDuckGo's first Wikipedia search result.
The default search engine keyword is "w". This can be changed on the Firefox search preferences page: about:preferences#search
Using DuckDuckGo instead of Wikipedia's native search will mostly avoid disambiguation pages and allows for far greater leniency in your search query (so your query doesn't need to match the exact Wikipedia page name).