I did it this way by accident : I installed chrome and logged into gmail. Chrome asked me if I wanted to make gmail the default mail app and I said yes.

I would have NEVER discovered that this would be even possible any other way. I don't know if it works on other browsers but it's cool that it works.

On right click in chrome I have two "search with DuckDuckGo" options and one searches on a new tab and another on the same tab. I don't know why.