How to enable TraceMonkey in Firefox 3.1 Beta 2

TraceMonkey is used by Firefox 3.1 Beta for faster JavaScript loading.It is faster than Firefox3 37.5 times.
Steps to try TraceMonkey:

• User must have Firefox 3.1 Beta 2 installed.
• Open a new tab
• type "about:config" and hit enter
• on the warning message,click "I'll be careful,I promise!"
• type in "jit" on the "Filter" tab.
• At the "Value" bar,change both "false" to "true" by double click it.
• Restart Firefox.