True, but since Windows (up until 7, and then on 10 as well) doesn't come with a PDF viewer by default, the only popular platform that guarantees a PDF viewer i

True, but since Windows (up until 7, and then on 10 as well) doesn't come with a PDF viewer by default, the only popular platform that guarantees a PDF viewer is OS X, which only makes up a small portion of Firefox users (7 percent as of 2009 [1], can't find newer statistics though), especially since Firefox is quite popular for GNU/Linux users. And anyways, it all comes down to convenience. I know of many people who would much prefer viewing a PDF in their browser than having to switch between applications even though they're "techy enough" to install one. If people are happy with the PDF.js or some other in-browser PDF viewer, why make them switch? [1] https://www.cnet.com/news/only-7-percent-of-active-firefox-browsers-running-on-macs/ https://www.cnet.com/news/only-7-percent-of-active-firefox-b...