Firefox may block downloading of a file through unencrypted http:
protocol if a link is opened from a https: page (HTML version of the
Org manual served from orgmode.org this case). The problem with CTAN
mirrors is that not all hosts have TLS certificates including their
CTAN names.
I can't figure out how to link to the babel documentation in a way other
than a link to CTAN. If this might be an inconvenience (due to https
issues), perhaps we could simply put in the documentation something like
'see the Babel docs', or referencing the command 'texdoc -M
babel', which opens the locally installed babel documentation. The
problem is that not all GNU/Linux distributions include the
documentation in their versions of TeX live. For example, Arch Linux
does not include documentation in the official repos and must be
installed separately via an AUR package.