You'd implemented
ZeroHour's fix, I guess -- that's what I had done, and it had worked for me.
I had also edited markers.xml to get rid of troublesome XML-breaking characters in it, getting rid of ? and & and the like.
If you have Firefox, you can do some debugging with it by selecting
Tools > Error Console
Any HTML, CSS, or JavaScript errors will show up there.
If you are more adventurous, you can go to the
Firefox add-ons page and install the JavaScript debugger and try to use it to see what's happening.