The table copied from excel and pasted into a div with contenteditable=true misses its wrapping <table> element.
Open an excel document, copy a table, say a 2*3 table holding 1, 2, 3; 4, 5, 6. Go to the http://jsfiddle.net/ThinkingStiff/AbKTQ/. Paste the content into the text field which contains "I look like a textarea". Press F12 and then check the html of that control, you will see the content in the attached image: Under the div, there is no table element but only the colgroup and tbody which are sub elements of the table.
Since table contains the format information, it should be available after paste operation. Both IE and Chrome can handle this correctly. Hope Firefox can do the same.
Both 38 and 39 have the same problem.