Firefox before 1.0 and Mozilla before 1.7.5 allow inactive (background) tabs to focus on input being entered in the active tab, as originally reported using form fields, which allows remote attackers to steal sensitive data that is intended for other sites, which could facilitate phishing attacks.
secunia.com/advisories/12712
secunia.com/multiple_browsers_dialog_box_spoofing_test/
secunia.com/multiple_browsers_form_field_focus_test/
www.mozilla.org/security/announce/mfsa2005-05.html
exchange.xforce.ibmcloud.com/vulnerabilities/17789
oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A100053