The next version of Firefox is to be Firefox 3.0, which is scheduled to be released later this year. It will be able to detect malicious code on Web sites that users are trying to access.
The plans could change before release, but right now the plan is for an interface that will warn users that the pages they are trying to access are dangerous. Plus the malicious page wouldn't be able to load. Firefox technicians are debating whether there should be an override mechanism that would allow users go to malicious pages no matter how dangerous.
There are now more than 30,000 new malicious Web sites a day as many hackers move away from using e-mail to do their dirty work and turn to malicious sites. Sometimes they make their own sites, but most of the time they hack into legitimate sites and embed malware into them.
There are more details and you can get them at this link
Mozilla Aims To Warn Users About Dangerous Sites -- Security -- InformationWeek