It was reported that service workers intercept responses to plugin network requests made through the browser. Plugins which make security decisions based on the content of network requests can have these decisions subverted if a service worker forges responses to those requests. For example, a forged crossdomain.xml could allow a malicious site to violate the same-origin policy using the Flash plugin.
This issue is addressed via the following Fedora security advisories:
This issue does not affect the versions of Firefox shipped with Red Hat Enterprise Linux 5, 6 and 7.