This appears to be fixed upstream for Firefox 27/28. See: https://bugzilla.mozilla.org/show_bug.cgi?id=861266
As a workaround, you can enable TLS 1.2 in Firefox/Iceweasel 25 and 26 by setting the preference security.tls.version.max=3 in about:config.
See: https://bugzilla.mozilla.org/show_bug.cgi?id=861266#c27 -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
