The extension allows you to configure the toolbar button as a shortcut for quickly searching with a single search engine or a group of search engines. The toolbar button opens a popup by default, where you can select a search engine, and there is also a button for opening the extension's options.

Though that's not the standard way of accessing a browser extension's options, it was just added to the popup as a convenience. All browsers have buttons for opening options on the management pages of extensions. Visit about:addons to open the options page of your extensions.