Not sure I undersand. Mozila Firefox is a browser. Allows you to connect to the internet through a medium. A search engine is; Dogpile, Ask, Google etc. You should have the option of using a search engine on the top right in Firefox.
Which ever site you like you can 'bookmark' from the toolbar at the top of Firefox browser. It's called 'bookmark' for ease of use presumably. From there the dropdown menu will ask where you wish to err bookmark that site.
Hope that helps.