A dangerous security flaw has been found lets hackers and malware bypass the Secure Sockets Layer (SSL) of these browsers. SSL is a very common security feature that protects the privacy and integrity of information as it's sent between your browser and a server. The Heartbleed bug also let hackers walk right through SSL.
This bug also has an ominous name: BERserk. The BER stands for Basic Encoding Rules. It was discovered by Intel's Advanced Threat Research team and a French cybersecurity expert. Hopefully this won't get overshadowed by the also very dangerous Shellshock vulnerability, which was announced the same day.
BERserk is just as dangerous. It's present in all previous versions of Firefox and Chrome, although there is no evidence that it's been exploited for malware attacks yet. That's good news, because it's very easy to fix this problem. In fact, you may have already fixed it!