How can I turn off searching from address bar?

You can turn off the web search in the address bar by changing a preference.

Note: This preference does not affect smart keyword searches from the Location Bar. In the Location bar, type about:config and press Enter. The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise! to continue to the about:config page. In the Search field, type keyword.enabled. Double-click the keyword.enabled preference to set its value to false.