There have been times that Ive been absolutley dumbfounded by the absence of the style drop down list in the back end when editing or writing content. Everytime it disappears it makes me think for a while about where it could have possibly gone ... so Ive written this very short tip in the hope to remind myself and to help others:

Make sure that the url in the browser is the same as the livesite - for the most part you have to remove the www from the address.

When I remember this they instantly re-appear .... magic! This also goes for when the popups like the html editor and hyperlink editors dont display properly also.