That's.......... actually not a bad answer to my question, goddamnit ;)
BUT: you do have to concede that it's not a technical reason. It boils down to "Adobe are goddamn useless, let's just do their job for them because it will make our life a bit easier". There's no requirement for pdf viewing in the HTML spec or anything like that. It's not required for web browsing and it doesn't really have any place in the browser in a technical/engineering sense - from an "engineering purity" perspective these two things should be separate, even if you do like your pdf viewers written in javascript. The "correct/pure" engineering solution would have been for them to bundle their awful javascript pdf viewer in an electron(ish) app and release it as the "google pdf viewer", with all the requisite spam in gmail and the technical press, and to have chrome default to it if it's installed. Hell, you could make it a separate application and still bundle it with chrome.
There must have been a LOT of support enquiries about "the adobe doesn't work" for it to survive a cost/benefit analysis for implementing an entire pdf viewer. That's not a trivial piece of work that somebody churned out in an afternoon (despite the performance of the thing feeling like it ;) )
If I was that product manager, I would not make that decision lightly. First I'd have built a special page into my support area that redirects the user to adobe.com/support if they type "pdf" or "adobe" into the "search support" bar. (You know what I mean - you've seen it in action on help desk sites where they try to fob you off rather than just giving you a "contact us" box straight away).
This is all a whole lot easier to implement than a pdf viewer. In fact if you're using something like zendesk you get it for free. For me to decide to build a pdf viewer into my browser, I'd have to be getting a high volume of support emails about it after I'd implemented the change above.
I don't think that's what happened.
In the post i largely ignored, you said:
>Multiple web browsers have embedded PDF viewers because the PDF viewing experience for most people sucked so much
Allow me to give you an alternate explanation / interpretation, which I admit might come across as "a little bit cynical" or paranoid, but which I believe to be more fully borne out by the facts than the "cost/benefit analysis" theory you advocate. I don't think "multiple browsers" did that at all. Here's my theory:
1. Google decided to build a pdf viewer into chrome because they were busy trying to turn chrome into an operating system (see also: chrome os), and they knew that would mean including a pdf viewer, since a pdf viewer is a fairly essential tool for an operating system if it wants any kind of mainstream adoption. This had the added side-effect that for many users their pdf viewing experience would improve, because adobe are basically incapable of doing software. So it was really a "two-fer" for google.
2. Mozilla, seeing google's announcement for a pdf viewer built into their browser, did what Mozilla has been doing for the past decade: copy Chrome without giving any thought at all to any of the considerations you and I are discussing today. Or indeed any consideration other than "what is google doing with chrome this week?".
Now, I do try to keep my paranoia and cynicism in check, but to me this seems like a far more likely explanation. Perhaps I'm wrong. It would be kind of nice if I was. If you have some data to support your theory I'd love to see it.
I don't have much data to back up my theory. I can't be bothered looking into what chrome's support site was like pre-pdf-support. But I do have one data point: I can confirm that chrome added pdf support first, with Mozilla aping them almost immediately (they were pretty much at parity within a year or two).
Maybe Mozilla had coincidentally already done a full cost/benefit analysis of adding a pdf viewer before google went live with theirs. It's not impossible. But it seems a little unlikely to me.
;)