why is yslow not showing the page load time

so I installed yslow firefox extension and it's on my statusbar...but it's not showing any page load time info and just says开发者_如何学Python 'yslow' whenever I go to any page

do I have to do some configuration or something?

what am I doing wrong?

Check the YSlow User Guide for a walk-through of using the Firefox extension.

If you're having trouble making the Firefox extension work, you can also try the bookmarklet version.

Activate the Fire bug by hitting F12 key and after that you will be able to view the response time along with YSlow icon in status bar.