Keeping in mind it's been a few years (my last day at Mozilla was in mid-2015), and I was in the web dev org, not the browser... The sheer number of platforms,

Keeping in mind it's been a few years (my last day at Mozilla was in mid-2015), and I was in the web dev org, not the browser... The sheer number of platforms, variants, etc. of the browser and the number of test runs that need to happen are mind-blowing. So it's entirely within the realm of believability for me that the mozbase packages (which provide a lot of the foundation for all of that automated infrastructure) could hit the most-downloaded list. It's not that Mozilla is necessarily that much bigger than other big-name tech companies, it's just that Mozilla open-sources everything by default and puts most stuff on PyPI. As an aside, though, I think people do tend to underestimate the scaling stuff Mozilla deals with. Once I got to give a conference lightning talk pointing out we could probably claim the highest-traffic Django deployment in the world, for example (the version check done by Firefox on startup, if you're curious, is or at least was a Django-backed service). Though I'm pretty sure Instagram has taken that title now; back in 2013 when we talked about that we "only" served on the order of a billion requests/day :) Even things like MDN -- which is what I worked on in my time there -- presented interesting challenges. Building a wiki with the kinds of features technical writers need, that's still responsive and fast to build and render the pages post-edit and capable of handling the traffic of a top-300-ish (Alexa currently puts MDN at #107 worldwide) site, isn't entirely simple to do.