A seven year old vulnerability has been re-introduced in Mozilla and Firefox, which can be exploited by malicious people to spoof the contents of web sites.
Secunia has constructed a test, which can be used to check if your browser is affected:
http://secunia.com/multiple_browsers_frame_injection_vulnerability_test/
The vulnerability has been confirmed in Firefox 1.0.4, Mozilla 1.7.8 and has been confirmed in Camino 0.8.4, but does not affect version 0.8.3. Other versions may also be affected.
SOFTWARE:
Mozilla Firefox 1.x
Mozilla 1.7.x
Camino 0.x
SOLUTION:
Do not browse untrusted web sites while browsing trusted sites.
VERIFY ADVISORY:
http://secunia.com/advisories/15601/
http://secunia.com/advisories/15602/
Secunia Security Advisories
http://community.securityteam.us/article.php/20050607101904889