[Feature] Add OpenSearch protocol support

[RobotoSkunk]

I'm moving from Chromium to Firefox because I need to work with the tools that ships with Firefox and it suites more with the things that I do, but something that I've found is that this website doesn't complain with OpenSearch protocol, so I can't use this in Firefox via URL.

My idea is adding support for the OpenSearch protocol to add support for Firefox's URLs.

https://github.com/dewitt/opensearch