Mozilla developer Matthew Noorenberghe reported that whitelisted Mozilla domains could make UITour API calls while the UI Tour pages for Firefox are present in background tabs. If one of these Mozilla domains was compromised and open in another tab, an attacker could then use that tab to engage in spoofing and clickjacking in any foreground tab.
Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Matthew Noorenberghe as the original reporter.
This issue does not affect the version of firefox and thunderbird as shipped with Red Hat Enterprise Linux 5, 6 and 7.