Java has yet another security vulnerability. Details on exactly which versions of Java are sketchy at this point, but all versions of Java 7 from Oracle are... if you have such a version of Java, turn off Java in your web browser ASAP!
Of course, both Apple and Mozilla have acted quickly to disable all versions of Java up to the latest version of Java 7. The only way you'll get a Java applet working with Safar or Firefox is to wait for Oracle to update Java, or if you take certain other unsafe procedures to get a vulnerable version of Java working again.
Kudos must be extended to both Apple and Mozilla in this case for making a choice that has made some users angry. This vulnerability was being actively exploited to drop malware onto Windows users' systems, and it was just a matter of time before Mac users were similarly affected. The fact that they acted so quickly to protect users from this threat shows that security is of utmost importance to both companies.