Firefox is your browser(like Google Chrome, Internet Explorer etc) and Google is set as your search engine(like Bing, Yahoo etc) - different functions. I presume you are entering a search term in which case this is normal behavior. If you are entering a full website URL(ending with . com or similar) in the address(location, URL) bar, Google shouldn't be involved. You can go to Options>General to make sure that Firefox is set as your default browser. Any search term entered will show your selected search engine.

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