Hello,
You can change or add a search engine for the search toolbar in Mozilla FireFox by clicking on the button to the left of the search field, and clicking
Manage Search Engines.... You'll see a list of installed search engines. You can add a new search engine by clicking on the
Get more search engines... link below the list.
Alternatively, you can go straight to the following FireFox Add-on page to add a search engine:
https://addons.mozilla.org/en-US/firefox/browse/type:4