It would be useful to disable IPv6 for this connection and try again.
So applied the command proposed by Ed as root:
$ echo 1 > /proc/sys/net/ipv6/conf/(name of interface)/disable_ipv6
and now I never have any error, the page always shows in firefox,
konqueror or chrome.
Also openssl s_client -connect docs.python.org:443 seems to always
succeed (attached is the output of tcpdump).
In your opinion, is this an issue with fedora or with my ISP (which is OVH)?
Frédéric