There has been really quite alot
of discussion about
a DDG browser
(you can click on those words individually, they're ALL different links). There's even a thread, posted by Zac, titled "[b]Please don't ask about a DuckDuckGo browser[/b]."
Other than date searches this
has got to be the most
asked about thing on duck.co.
DDG has been included in lots of browsers and OSs. I guess the reason one doesn't see it in so many is because there are lots of alternative browsers but only one DDG and one Google (and Google is way more famous). Just looking at DDG's Wikipedia page I can see that it's in Gnome and Pale Moon. Then, of course, it's in Apple's Safari and Mozilla's Firefox.
Firefox for Ubuntu has included DDG for years now (long before Mozilla jumped on). Though a bit of a memory hog (right now with three windows open, it's using about 25% of my memory), Firefox for Ubuntu is fast, clean and simple. Not at all bloated in my opinion.
I agree, there are lots
of alternatives to Firefox. (Since you mentioned IE, I'm going to mention Edge, Microsoft's next browser.) You could check out Chromium from which Google's Chrome is drawn (it's like pure browser before they insert the evil). Then there's the Opaque private browser by community leader, Javathunderman
Then there are a whole bunch of re-branded and improved versions of Firefox which you touched upon.
I like Firefox because of it's developer toolkit, it's parent Mozilla, it's customizability and it's awesomeness. One of the things to try out might be a faster computer (probably to expensive, skip that).
But no matter what browser we use, I think we can both agree that we want the world to use DDG.