Why would you want to install an addon for a feature that's been available in FF and has been available for a good 3 or 4 years? Go to preference > search. Scroll down the Search page until you hit One Click Search Engines. Choose the search engine you want to put a hotkey for, next to it you'll find a Keyword column. Put the keyword you want. If you want to reproduce the experience of this plugin, set DuckDuckGo's keyword to: ?k - though personally I would use d for duckduckgo, g for google, y for youtube, e for ebay, a for amazon, ff for firefox addons etc. Don't forget that you can add more search plug-ins through mycroft project's website.

I loved the SDK version, for allowing me to have two search engines at hand. I understand that there are MANY limitations on the WebExtensions, compared to the SDK.

Hopefully, when those limits will be relaxed, this extension will become usable again. But until then, this extension is pretty much useless, as searching by keyword is already implemented (and configurable) in the basic Firefox installation.

Thank you for all your work.