For OS versions below 10.7..."Apple supplies their own version of Java. Use the Software Update feature (available on the Apple menu) to check that you have the most up-to-date version of Apple's Java for your Mac." - From the Java website.
In Firefox: Look at the very top left of the browser window. If you don't see a Menu with the Tools button on it, tap the Alt key and the menu will appear.
and then make sure that there is a check mark in the box beside Accept cookies from sites