Works fine here on FF11/XPSP3 Rated 5 out of 5 stars

Reading other users' reviews I hesitated to install this StatusbarEx :) Works just fine here, moreover together with url-addon-bar add-on I have all StatusbarEx data right in the navigation bar (wide screen).
Perhaps I would appreciate having the option in 'Memory Usage' to split system free ram and Firefox ram usage, but it's not a major point.
UPDATE : Works fine here on Firefox 12 (still XPSP3) as well :)