Here are the step-by-step instructions for majority of the browsers.  Java and JavaScript are two different things, please make sure that you're looking at the correct language.

WARNING: Please note that you may loose some of the web page functionality by disabling JavaScript.

Navigator 3.x

• Go to "Options | Network Preferences..." from the main menu
• Change to the "Languages" tab
• To enable: make sure "Enable JavaScript" check box is checked
  To disable: make sure "Enable JavaScript" check box is unchecked
• Restart the browser

Communicator 4.x

• Go to "Edit | Preferences..." from the main menu
• Select "Advanced" panel
• To enable: make sure "Enable JavaScript" check box is checked.
  To disable: make sure "Enable JavaScript" check box is unchecked.
• Restart the browser

Explorer 3.x

• Go to "View | Options..." from the main menu
• Change to the "Security" tab
• To enable: make sure "Run ActiveX scripts" check box is checked
  To disable: make sure "Run ActiveX scripts" check box is unchecked
• Restart the browser

Explorer 4.x

• Go to "View | Internet Options..." from the main menu
• Change to the "Security" tab Select "Custom" and click on the "Settings..." button
• To enable: make sure "Enable" is selected under "Active scripting"
  To disable: make sure "Disable" is selected under "Active scripting"
• Restart the browser

Simply reloading the page, rather than restarting the browser, maybe sufficient under some browser versions.