Boy you are fast! Yes I was browsing other themes and switched it back right after my last post, but after you got there.
I am not sure I understand the explanation? Are you saying that even though I closed those two missing closing divs, I might have done it in an incorrect place so even though they are closed, they are still incorrect?
Also why would taking out the sidebar on the single post page cause the display problem in Firefox, but still display correctly in IE?
I notice this same display problem occurring on another site using this theme. In that case, it only stayed that way for a moment until the page finished loading. There seemed to be a momentary glitch each time the page would load, but once it got past the stall and loaded it displayed OK. This made me think maybe the page I am having trouble with is not finishing loading? Make any sense at all?