How change the firefox web search engine type?

When i put some word, lets say youtube.com but i just put youtube on the navigation bar. And the result it didn't direct me to youtube.com, but it directs me to the ask.com. Before this happens, if i just put youtube,it will directs me to youtube.com and it use google. How to change it back to before?

Thnaks in advance.

 

A very simple way is to look at the far right of the navigation toolbar, where the Search Engines are. If you have the blue G, the default search engine is Google. Ask.com is in my list, but I can place it in the dropdown, initiated by clicking on the down arrow to the right of the symbol. Ask.com is red in color.

 

thanks Tonyt, that is what i want.