Security researcher Masato Kinugawa reported that opening a target page using a POST to the url prefixed with the feed: protocol disables the mixed content blocker for that page. This could allow for the risk of a man-in-the-middle (MITM) scripting attack on pages that accidentally include insecure content which would otherwise be blocked. 


External Reference:

https://www.mozilla.org/security/announce/2015/mfsa2015-86.html


Acknowledgements:

Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Masato Kinugawa as the original reporter.

Statement:

This issue does not affect the version of firefox and thunderbird as shipped with Red Hat Enterprise Linux 5, 6 and 7.