Internet Explorer: Choose Tools (from the top menu) -> Internet Settings -> Security tab. Set Zone Security Level to medium.
Mozilla Firefox: Choose Tools (from the top menu) -> Settings -> Content tab. Put a tick to 'enable javascript' option.
Opera: Press CTRL+F12, or choose Tools (from the top menu) -> Settings. Choose Expert tab -> Content option. Put a tick to 'enable javascript' option.
Safari: Press CTRL + , (CTRL + Comma) or choose Edit (from the top menu) -> Preferences. Under Security tab put a tick to 'enable javascript' option.