It happens to me too on Debian, yet PDF.js works fine on my Nexus 7 (2012) table, even though the i7 is much faster than the Tegra 3. It's probably an hardware rendering issue.

A few other people on HN is not “the rest of the world”, particularly when most of the complaints either don't reproduce at all or are significantly less problematic than claimed.

It's dead certain that PDF.js has plenty of room to improve but that requires solid benchmarking, not anecdata. I would hope Mozilla is collecting telemetry data about common bottlenecks from millions of users and triaging to see which problems are core or artifacts from local system configuration, graphics drivers, etc.

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.