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?

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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.

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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.