Uses external service file.io I expected this to work completely offline, but it uses external service, which does have its own Terms & Conditions and Privacy Policy, by the way. Just read the source code of the addon, and T&C with PP of file.io to see if you're OK with that before using this addon.
Sadly there is no other way to get Firefox to accept a custom search engine, unless it's hosted on a HTTP/HTTPs website. I thought it was already quite obvious that the extension uses file.io, but I am working on making this even more obvious.
