An update may erase all the settings. In that case just go to Java's website to test and activate Java on your browser.
When Mac OS is updated to a newer version or updated for Java some users may experience this issue even when they've set this up before. This is a common issue for Mac users.

Steps to follow:

For Safari Browser

Step 1: Go to Safari > Preference > Security. Enable plug-ins/Enable Java/Enable JavaScript.

For Safari 5.x:

 

For Safari 6.x:

Step 2: Go to Java's website: http://www.java.com/en/download/testjava.jsp and follow up the steps.

Step 3: Close the browser and restart the browser.

• For Firefox browser

Step 1: Go to Firefox > Tools > Add-ons option to enable Java plugin.

Step 2: Go to Java's website: http://www.java.com/en/download/testjava.jsp and follow up the steps.

Step 3: Click the plugin icon on the address bar, then click the Allow and Remember button.

• For Chrome

Step 1: Go to chrome://plugins to ensure that Java is enabled. You may want to ensure “Always allowed” is ticked.


 

Step 2: Go to Java’s website http://www.java.com/en/download/testjava.jsp and follow the steps to confirm Java is working and that you have the latest version.