Short Search от Willian Carlos da Silva

To use, type ']' followed by the engine shortcut name, e.g., ] yt <search>, for search on YouTube, or just ] <search> for search on the default defined engine in the options page.
Use the options page of the addon to add engines using %s as the search placeholder and a shortcut name for it.
The last search term can be reused in the next searching just typing ] <shortcut engine>.