In Firefox you can add a search keyword to prepared bookmarks to use tags for searching specific sites.

For example, you can store https://en.wikipedia.org/w/index.php?title=Special:Search&search=%s as a bookmark Wikipedia Search with the keyword w, you can then type into the address bar w Test and it will redirect you to the Wikipedia search page searching for Test.

In the URL, the %s is the search text placeholder. You can use any URL and prepare it as a search bookmark.

Search Links

You can drag and drop these into your bookmarks, or open them and then store them, adding a keyword.

Name	URL	Suggested Tag
Dictionary.com Search	http://www.dictionary.com/cgi-bin/dict.pl?term=%s	dict
AlternativeTo.net Search	https://alternativeto.net/browse/search?q=%s	alt
IsThereAnyDeal Search	https://isthereanydeal.com/search/?q=%s	deal
Wiktionary Search	https://en.wiktionary.org/w/index.php?title=Spezial:Suche&search=%s	word
Wiktionary (DE) Search	https://de.wiktionary.org/w/index.php?title=Spezial:Suche&search=%s	wordde

Developer Resource Search

Name	URL	Suggested Tag
MDN Search	https://developer.mozilla.org/en/search?q=%s	mdn
MDN HTML Search	https://developer.mozilla.org/en-US/search?topic=html&q=%s	mdnhtml
MDN CSS Search	https://developer.mozilla.org/en-US/search?topic=css&q=%s	mdncss
MDN JS Search	https://developer.mozilla.org/en-US/search?topic=js&q=%s	mdnjs
MDN API Search	https://developer.mozilla.org/en-US/search?topic=api&q=%s	mdnapi

Administration Resource Search

Name	URL	Suggested Tag
Man Pages Man.cx search	https://man.cx/%s	man
Cheat.sh TL;DR command reference	https://cheat.sh/%s	tldr