I noticed that the two bugs they linked [1] [2] are both due to the distros introducing bugs by applying patches -- one for hurd support (!) -- that were not shipped by the upstream projects that the distros were repackaging. As we have discussed earlier [3] I think the way distros inject themselves into this software development process produces these bad outcomes due to getting the incentives wrong.
[1] https://bugzilla.mozilla.org/show_bug.cgi?id=1679430
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1633467
[3] https://news.ycombinator.com/item?id=26216917