Currently when you want to use a secondary engine for a search, you click the drop down, click the engine, then click enter on your keyboard. Pressing enter is unnecessary, because the browser doesn't save the currently selected search engine. You have to reselect it every time.
To promote ease of use, the browser should either A:immediately initiate the search when it's icon is pressed, or B:save the selected search engine for as long as that specific browser tab persists.