Hyperbole does not lead to anything useful.<p>You might not consider Chrome to be open-source by your personal definition of the term but that&#x27;s fine hair splitting: you can submit a patch to Chromium and some weeks later millions of Chrome users are running it; you&#x27;re similarly free to fork chromium and make significant changes while still pulling in code from upstream. Yes, license nerds can argue about philosophical meanings but it&#x27;s far from the closed-source world of IE&#x2F;Trident, Opera, etc.<p>&gt; Mozilla had to build a PDF reader from scratch (pdf.js), it couldn&#x27;t just reuse what Chrome was using to display pdfs, since it wasn&#x27;t open source<p>That&#x27;s a single, separate component which, as comex pointed out, was licensed from a third-party vendor and nicely illustrates that Chrome is in fact open-source: the only reason it wasn&#x27;t an option is because it wasn&#x27;t part of the open source Chrome codebase.<p>You&#x27;re also leaving out a key part of the pdf.js (and Shumway for Flash) story which was people at Mozilla trying to demonstrate that you could write complex renderers inside the JavaScript environment and sharply reduce the amount of exposed C&#x2F;C++ code. I suspect they would have gone with pdfium had it been available but the security improvements would still have made that decision non-trivial.