Installed Firefox Beta and now Bing is default search engine in location bar

There's a plugin for Safari called Glims that lets you add different search engines (including Wikipedia) to the search bar among other tweaks. You can read about and download it here.

Here's a post on someone's blog that details how to install it and set your search engines to what you want.

Hope that helps!

The AnySearch extension allows you to set any search engine you want.

It achieves it by listening to the beforeSearch event, canceling the default behaviour and checking your settings for your chosen search engine. Then it puts your query into the specified search engine and displays the results.

You could, too, edit the host file, redirecting form any of the default search engines to the one you want, but that wont be so neat.