I have installed the latest versions of YSlow and Firebug into the latest version of Firefox on Windows 7 (and restarted Firefox), but when I click on YSlow nothing happens. Also, when I click on Firebug, it opens but has no YSlow tab. I have disabled all other Firefox plugins and played with right-clicking YSlow and clicking run once and auto-run.
What am I doing wrong?
As a temporary solution, try using the YSlow bookmarklet.
It's an equivalent of regular YSlow.