Basically, Firefox allows you to set a keyword (which I often set to an abbreviation + question mark) which you can link to a site's search URL. For example to search Google Scholar I would type my keyword, "sch?" and then my search query, and after pressing enter I am taken to the site's search results. It's a few more steps you have to take, but has the added benefit of allowing you to add the functionality for any site.
Alternately you can switch the default search engine to DuckDuckGo, which lets you use DDG's "bang" search shortcuts (see https://duckduckgo.com/bang) from the Awesomebar. So you just type a search query and then append "!g" to run that search query through Google, "!w" to search for it on Wikipedia, "!yt" to search for it on HN, etc.
https://www-archive.mozilla.org/docs/end-user/keywords.html
Basically, Firefox allows you to set a keyword (which I often set to an abbreviation + question mark) which you can link to a site's search URL. For example to search Google Scholar I would type my keyword, "sch?" and then my search query, and after pressing enter I am taken to the site's search results. It's a few more steps you have to take, but has the added benefit of allowing you to add the functionality for any site.