I had a problem with one particular page doing that too, adeh awhile back? However I then changed to NOF9 and mine seems ok again -atleast on Opera; Firefox is on my other pc so I'll check that later. But would be interested to hear, like barryoneoff, what NOF say about this issue.Will go and check out that thread you started barryoneoff.
It shouldn't matter what software you're using as long as the code is sorted. I had some trouble with layers centering, but did eventually manage to crack it. If it is this that's the problem I'll post what worked for me.
The other limitation with NOF is that until you publish your site - locally or remotely - there is no HTML to edit as such, and there is no inbuilt editor, only a viewer. Certain elements of code can be added to for certain parts of the content when in page view, but not much.
I would have to download the server content, edit it somehow and then reload it. Beyond my skills.