(In reply to Botond Ballo [:botond] from comment #8)
I actually don't see this anymore, even before the fix of bug 1508177, modulo the fact that the page is slightly horizontally scrollable, even before tapping on "Contributors" (which I think is bug 1526940).
(In reply to Botond Ballo [:botond] from comment #9)
The bug 1526940 behaviour was not present before, but is now, replacing the original bug here.
The behaviour seems to have changed sometime between 68 and 69. Unfortunately, due to bug 1573207, I'm not able to find a window for it.
I see now what was confusing me: on a tablet, even though the site sends the same content with or without "Request desktop mode", the behaviour is different. The "bug 1526940 behaviour" only occurs with "Request desktop mode", and the behaviour which is the subject of this bug only occurs without "Request desktop mode". The latter was indeed fixed by bug 1508177 as expected, although the change made in bug 1508177 is Nightly-only for now.
I'm going to update the dependency from bug 1508177 to bug 1571599, which tracks shipping the behaviour change on all channels.