Ask HN: Firefox cannot display PDFs correctly?

This is nothing new. It has been happening since Firefox first added their "in-browser" PDF renderer. The in browser renderer does not handle the full gamut of the PDF spec (the actual PDF spec. doc. is on the order of 800+ pages long) so whether a PDF renders, or not, depends upon what portions of the PDF spec. it utilizes.

This is what the warning "this doc may not be displayed correctly" really means. It is saying: "this PDF uses PDF features we do not yet support" (but without being so explicitly direct about the meaning).

But barring a recent bug that has broken everything, the cause is inside the particular PDF's because they use features that FF's render library does not yet support.

i already saw those warnings a few times also, but i never noticed any difference.

Can you provide any examples?

i always thought that probably they're just being cautions...

There is one thing they don't have enabled by default (at least it wasn't the last time i checked), however, that may also bring that warning up: PDF Forms.

You can enable them in about:config searching for pdfjs.renderInteractiveForms and setting it to true (but they probably have a reason not to).

This will enable you to fill pdf forms directly in the browser.

PDF.js is actually a very good tool. It's actually (again, the last time i checked) more powerful than Chromes's PDFium

You probably won't find this a particularly helpful response, but no, I have not experienced any such issue.