Rated 4 out of 5 stars
MUCH more usable. Thanks.
My only nit is that it's impossible to know what folder you are dropping a message on to. In case anyone would like "drag and drop feedback" to indicate which folder you are dropping a message into, here's my userChrome.css. Too bad for me that it took 2 hours of digging to realize that I needed to have "!important" in the rule!
* Do not remove the @namespace line -- it's required for correct functioning
@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* set default namespace to XUL */
tree[seltype="cell"] > treechildren::-moz-tree-cell-text(dropOn),
tree[seltype="text"] > treechildren::-moz-tree-cell-text(dropOn),
background-color: #bebebe !important;