Firefox has built-in support for Keyword Search bookmarks. You don't need to install an add-on to create aliases.

If you bookmark any website's search results page, you can add a keyword and edit the bookmarked URL to include a printf-style %s placeholder. When you enter the keyword plus some string, Firefox opens the bookmarked URL, substituting your string for %s.

For example, I have a "w" keyword search for Wikipedia https://en.wikipedia.org/wiki/index.php?search=%s and a "yt" keyword search for YouTube https://www.youtube.com/results?search_query=%s&search=Searc...

Awesome, that's exactly what I was looking for.

If you mean going to the address bar, typing wiki [tab] and getting a search of wikipedia for whatever you type next, then yes. See this article on how to do it: https://support.mozilla.org/en-US/kb/how-search-from-address....