The Javascript "Same Origin Policy" (SOP), as implemented in (1) Netscape, (2) Mozilla, and (3) Internet Explorer, allows a remote web server to access HTTP and SOAP/XML content from restricted sites by mapping the malicious server's parent DNS domain name to the restricted site, loading a page from the restricted site into one frame, and passing the information to the attacker-controlled frame, which is allowed because the document.domain of the two frames matches on the parent domain.
Netscape Mail Notification (nsnotify) utility in Netscape Communicator uses IMAP without SSL, even if the user has set a preference for Communicator to use an SSL connection, allowing a remote attacker to sniff usernames and passwords in plaintext.
When Javascript is embedded within the TITLE tag, Netscape Communicator allows a remote attacker to use the "about" protocol to gain access to browser information.