If you actually read that thread, you'd notice that many people confirm that lots of pdf's render just fine, and that it's specific workloads where pdf.js lags.

Frankly, it's something I'll gladly put up with in most cases just to avoid bad font rendering - and that's exactly what I do.

BTW, I'm pretty sure that this kind of stuff if pretty platform (and GFX-driver) dependent - and e.g. FF on mac os performs less well IIRC.