For others that search for this issue, I'd like to add that things are even worse worse with the editor when the ContentAreaMode property is "Div" (ie, inline editing). In this case the table cell management handles are positioned far away from the current table cell. This appears to have something to do with the display="relative" style on the content area div element. Using Firebug to change the value to the default "static", and the cell handles are positioned properly, although the table handles continue to be positioned horizontally offset from the table (which seems to be due to the centering of the table from the "margin:auto" style).
See the attached screenshots of the Telerik demo site editor (version 2011 Q2). The first shows the normal situation using Firefox (version 5 now) with all the table handles out of position when editing in the div mode; the second shows identical to the original post after I used Firebug to change the position style on the content div from relative to static. The edit handles are circled in the red boxes, and the current position of the cursor is shown with the vertical red line.
Is there a need for the div element to have "position:relative"? The cell handles are misaligned both horizontally and vertically; at least the table handles were only misaligned horizontally when centering, and still relatively easy to access.
For reference, this appears to be mozilla bugilla bug 399046
, which has not had progress in years. There is a comment that it originated in the Netscape code (!).