User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:57.0) Gecko/20100101 Firefox/57.0 Build ID: 20171019140425 Steps to reproduce: There is no support for webextensions to change the default (or add a new) search engine using the manifest API. "chrome_settings_overrides": { "search_provider": { "name": "DefaultSearch, "search_url": "https://www.google.com/search?q={searchTerms}", "is_default": true } References: https://developer.mozilla.org/en-US/Add-ons/WebExtensions/Differences_between_desktop_and_Android#Other_UI_related_API_and_manifest.json_key_differences https://developer.mozilla.org/en-US/Add-ons/WebExtensions/manifest.json/chrome_settings_overrides#Browser_compatibility

ni the expert for this:)

I can confirm that this feature is not yet implemented on android, it is only on desktop. As you can see, it is registered only at browser level https://searchfox.org/mozilla-central/source/browser/components/extensions/schemas/chrome_settings_overrides.json The extension used for testing was: https://addons.allizom.org/en-US/firefox/addon/youtubesearch/ Please see the attached video.