Press Windows logo key + W to open the Search charm to search settings OR Drag the Mouse pointer to the bottom-right corner of the screen, then click on the Search icon.
In the search box enter Java Control Panel
Click on the Java icon to open the Java Control Panel.
Windows XP
Click on the Start button and then click on the Control Panel option.
Double click on the Java icon to open the Java Control Panel.
Find the Java Control Panel on Mac
Launch the Java Control Panel on Mac OS X (10.7.3 and above)
Click on Apple icon on upper left of screen.
Go to System Preferences
Click on the Java icon to access the Java Control Panel.
Security tab: Allows you to configure various settings related to security such as grant permissions to content, alert users about site certificates, enable trusted publishers and blacklist revocation checks.
How to Enable Java on your browser
Firefox
Open the Firefox browser or restart it, if it is already running
From the Firefox menu, select Tools, then click the Add-ons option
In the Add-ons Manager window, select Plugins
Click Java (TM) Platform plugin (Windows) or Java Applet Plug-in (Mac OS X) to select it
Check that the option selected is Ask to Activate or Always Activate or on older Firefox versions, click on the Enable button (if the button says Disable, Java is already enabled)
Safari
Click on Safari and select Preferences
Choose the Security option
Select Allow Plug-ins, then click on Manage Website Settings
Click on the Java item, select an option (Ask, Allow or Allow Always) from the pull-down list When visiting other websites
Click Done, then close the Safari Preferences window