fixed #78

At last, it works pretty well with major browsers :D
There is still a little problem about user selection in IE8 when using the shift key for multiple selection (don't know how to disable it).

extensions/webmail/static/css/webmail.css

@@ -35,7 +35,7 @@ html > body #listing {
 }*/
 
 #emails th {
-    position: relative;
+    /*position: relative;*/
 }
 
 #emails th input {
@@ -116,10 +116,14 @@ th.selected {
 
 .draggable {
     cursor: move;
-    position: relative;
+    /*position: relative;*/
     border: 0;
 }
 
+.draggable img {
+    position: static;
+}
+
 .box li.dragging {
     background-color: #6AB0C5;
 }

extensions/webmail/templates/webmail/index.html

@@ -210,9 +210,6 @@
       th.addClass("selected");
     }
 
-    /* The IE way for disabling default selection */
-    $$("tbody>tr").set("unselectable", "on");
-
     var emails_table = new HtmlTable($("emails"), {
 	selectable: true,
 	shiftForMultiSelect: true
@@ -227,6 +224,10 @@
 	}
     });
 
+    /* The IE way for disabling default selection */
+    /* Actually it doesn't work :p */
+    $$("tbody>tr").set("unselectable", "on");
+
     bstart_dragging = function(item) {
         var block = new Element("div", {id: "draggeditems"})
 	    .setStyles({"position" : "absolute",