We have a grid that is correctly displayed in IE6 + IE7 but it is not even rendered in Firefox. When we look at the source code of the rendered HTML there is nothing in there for the grid. When we disable fixed headers the grid is correctly rendered in FF.
Any ideas?
This behavior doesn't sound right. I suggest that you submit a support request so that Developer Support can look into this in more detail. I suggest including a simple sample project, so that we know we're running the same code that you are.