diff --git a/content/treestyletab/treestyletabbrowser.js b/content/treestyletab/treestyletabbrowser.js
index 1f325712..97c0b0ef 100644
--- a/content/treestyletab/treestyletabbrowser.js
+++ b/content/treestyletab/treestyletabbrowser.js
@@ -2928,7 +2928,8 @@ TreeStyleTabBrowser.prototype = {
 		info.canDrop = true;
 		info.source = tab;
 		if (tab) {
-			var isCopy = this.isAccelKeyPressed(aEvent);
+			var isCopy = this.isAccelKeyPressed(aEvent) ||
+						(aEvent.dataTransfer && aEvent.dataTransfer.dropEffect == 'copy');
 			if (isCopy && 'duplicateTab' in this.mTabBrowser) {
 				info.action |= this.kACTION_DUPLICATE;
 			}