Firefox before 1.0 and Mozilla before 1.7.5 allow remote attackers to load local files via links "with a custom getter and toString method" that are middle-clicked by the user to be opened in a new tab.
Firefox before 1.0 and Mozilla before 1.7.5 allows inactive (background) tabs to launch dialog boxes, which can allow remote attackers to spoof the dialog boxes from web sites in other windows and facilitate phishing attacks, aka the "Dialog Box Spoofing Vulnerability."