To change the default search engine box on the top-right corner of FireFox:

This is how you can change it:

in the address bar of FireFox, type: “about:config”

In the box marked filter, type: “browser.search.defaultenginename”

Double click the value field or right click and choose Modify that value, by in the name of the search engine you wish to have as the default search engine. It must be one that you already have installed and also make sure you type in the name correctly.

Now if you type in “Yahoo”, restart Firefox and when your browser comes back you will see “red Yahoo Logo” and Yahoo as your default search engine box.

Then save that by pressing “Ok”.