The killer feature is that you can extend this with your own macros. E.g. if you want the address bar to recognize "hn " as a prefix keyword, and redirect "hn firefox address bar" to, say, Algolia — you simply create a bookmark with "Keyword": "hn" and "URL": "https://hn.algolia.com/?q=%s" (not actually a URL, don't click on it) – %s indicating where the macro parameter substitutes. Then "hn firefox address bar" macroexpands to
Or just right-click the input field, and if the browser recognizes it as a search field (they're good at it by default, but you can implement https://github.com/dewitt/opensearch to make extra sure), you'll get an option to create a search from it, with a keyword of your choosing (haven't tried Safari).