As of about a week ago, whenever I use LB for a DuckDuckGo search, the search page opens in Firefox, rather than my default browser, Safari.
This is regardless of whether Firefox is in the background, foreground or even when it hasn't been launched. LB will just open Firefox, and serve up the DDG search page.
I can confirm that the "default browser" check box is checked in Safari and unchecked in Firefox. Is this some kind of weird animal thing: foxes chasing ducks? If so, that's one crazy Easter egg!