Firefox:

You can globally enable/disable JavaScript by going to: Tools > Options... > Content > Enable JavaScript

Opera:

In Opera you can globally enable/disable JavaScript by going to: Tools > Preferences... > Advanced > Enable JavaScript

Microsoft Internet Explorer:

In MSIE you can globally enable/disable JavaScript by going to:

1. Tools > Internet Options... > Security tab
2. Under the Security tab, select the Internet Web content zone
   Under Security Level for this zone:
3. Click on the Custom Level... button at the bottom of the page
4. In the Security Settings window scroll down until you get to the section called Scripting (near the bottom)
5. Under Scripting > Active scripting, select the option marked Enable (or disable)
6. Click OK