When you click on an item's text in Firefox (tested version 3.0.9), like so:

 

 

...the subgroup expands and collapses quickly and shows a blip of the drop down in the top left of the screen and in the correct location also. You must click the plus to expand the group. I reproduced this on the sample page (http://cutesoft.net/example/general.aspx). Is there a workaround for this? A patch? We just upgraded to 6.3.