I strongly support this idea. Searching for years with #Startpage in all my devices. Firefox is my trusted browser for a long time. The two: #Firefox & #Startpage are buddys in private use of the internet. #Startpage should be neative integrated in to Firefox Search engines list. Out of my fiew, it have to be the default.
Although people committed to privacy can do this "by hand", it would certainly be an upgrade for those not willing to invest a little extra work. And also for those who are challenged a lot with setting IT things up.