Both predate #2222 and both are on master now, so they contradict the table
that PR added. One said the header flag keeps a reader signed in in any browser
configured to block third-party cookies; the other said the recommended
arrangement survives a reload whatever the browser's third-party cookie policy.
Firefox's block-all setting is the exception to both, because it discards
partitioned cookies as well, and the same table says so three lines away.
Folding them in here rather than leaving them to a separate pass, since this
branch is already editing the file.
Dmitry Verkhoturov
345eee8ba4