There are no problems displaying math symbols in pdf.js as of Firefox 58 and 58.1 on Mac OSX 10.13.3, but upon printing or being loaded in an external PDF editor via print preview, a bunch of math and greek symbols appear as boxes with question marks, as the wrong symbol (e.g. integral signs instead of brackets or omega instead of any other greek symbol), or just appear offset on the page. The font looks weirdly bolded as well. It seems a support issue was raised 2 years ago about this on the GitHub page, but was resolved in 2016. It appears like the new update has raised the old problem again.