There were a lot of Firefox users on Beta 44.
Usually this is a good thing. We like having a lot of users.
It wasn’t a good thing this time, as Beta had already moved on to 45. Then 46. Eventually we were at Beta 52, and the number of users on Beta 44 was increasing.
We thought maybe it was because Beta 44 had the same watershed as Release 43. Watershed? Every user running a build before a watershed must update to the watershed first before updating to the latest build. If you have Beta 41 and the latest is Beta 52, you must first update to Beta 44 (watershed) so we can better ascertain your cryptography support before continuing on to 48, which is another watershed, this time to do with fourteen-year-old processor extensions. Then, and only then, can you proceed to the currently-most-recent version, Beta 52.
(If you install afresh, the installer has the smarts to figure out your computer’s cryptographic and CPU characteristics and suitability so that new users jump straight to the front of the line)
Beta 44 being a watershed should, indeed, require a longer-than-usual lifetime of the version, with respect to population. If this were the only effect at play we’d expect the population to quickly decrease as users updated.
But they didn’t update.
It turns out that whenever the Beta 44 users attempted to download an update to that next watershed release, Beta 48, they were getting a 404 Not Found. At some point, the watershed Beta 48 build on download.mozilla.org was removed, possibly due to age (we can’t keep everything forever). So whenever the users on Beta 44 wanted to update, they couldn’t. To compound things, any time a user before Beta 44 wanted to update, they had to go through Beta 44. Where they were caught.
This was fixed on… well, I’ll let you figure out which day it was fixed on:
This is now the most satisfying graph I’ve ever plotted at Mozilla.