Change your default search engine in Firefox for iOS ...
support.mozilla.org › en-US › kbSee Enable or disable search engines on Firefox for iOS to change which search engines can be used for a search. Add a search engine. Tap the menu button at the bottom of the screen (the menu will be at the top right if you're using an iPad): Tap Settings in the menu panel. Tap Search. Tap Add Search Engine under the list of available Quick-Search Engines. Enter a name for the search engine in the Title text field.