Some WebExtensions providing search engines + suggestions with OpenSearch.
Signed XPIs are available in signed/
.
Works on Firefox 64, and should work on any later version.
The dummy provider is necessary because of https://bugzilla.mozilla.org/show_bug.cgi?id=1513459, unless you like having your keystrokes in the address bar sent over the network in real-time.
Google and the English Wikipedia aren't included for the moment since they currently come with Firefox and just need a keyword to be set.