When using the Nightly build on a MacBook Pro with Retina display (HiDPI), the built-in PDF viewer doesn't support native resolution. All content is rendered at half-resolution and scaled up, resulting in blurry output. In contrast, the pdf.js codebase itself contains a fix (see https://github.com/mozilla/pdf.js/issues/2222 and https://github.com/mozilla/pdf.js/pull/2283). Checking the live demo at http://mozilla.github.com/pdf.js/web/viewer.html displays a perfectly crisp text and graphics.

Presumably this issue will be addressed when the code you found gets merged into the tree. I don't know who in the "pdf.js team" to CC on this bug. I'll try to find out.

Steven -- bdahl is your guy.

Our fix will land the next time we update pdf.js in mozilla central which will happen at least once before FF19 uplift. It isn't the ideal fix, but it does improve the output quite a bit.

Fixed in bug 810107.