diff --git a/content/treestyletab/windowHelper.js b/content/treestyletab/windowHelper.js
index 6eeb52b7..5b2bb501 100644
--- a/content/treestyletab/windowHelper.js
+++ b/content/treestyletab/windowHelper.js
@@ -134,6 +134,7 @@ var TreeStyleTabWindowHelper = {
 			)
 			aObserver = aObserver.tabContainer;
 
+		if (typeof aObserver._setEffectAllowedForDataTransfer === 'function') { // Firefox 43 and older
 		TreeStyleTabUtils.doPatching(aObserver._setEffectAllowedForDataTransfer, aObserver+'._setEffectAllowedForDataTransfer', function(aName, aSource) {
 			return eval('aObserver._setEffectAllowedForDataTransfer = '+aSource.replace(
 				'{',
@@ -153,6 +154,20 @@ var TreeStyleTabWindowHelper = {
 				'$& TST.getTabFromEvent(event) == sourceNode &&'
 			));
 		}, 'TST');
+		}
+		else { // Firefox 44 and later
+			aObserver.__treestyletab__getDropEffectForTabDrag = aObserver._getDropEffectForTabDrag;
+			aObserver._getDropEffectForTabDrag = function(...aArgs) {
+				var effects = this.__treestyletab__getDropEffectForTabDrag.apply(this, aArgs);
+				if (effects === 'copy' || effects === 'move') {
+					let TSTTabBrowser = this instanceof Element ? (this.tabbrowser || this) : gBrowser ;
+					var TST = TSTTabBrowser.treeStyleTab
+					if (!TST.tabbarDNDObserver.canDropTab(aArgs[0]))
+						effects = 'none';
+				}
+				return effects;
+			};
+		}
 	},
  
 	overrideGlobalFunctions : function TSTWH_overrideGlobalFunctions() 
diff --git a/modules/tabbarDNDObserver.js b/modules/tabbarDNDObserver.js
index d75807e5..4db99d7c 100644
--- a/modules/tabbarDNDObserver.js
+++ b/modules/tabbarDNDObserver.js
@@ -968,7 +968,13 @@ try{
 		var info = this.getDropAction(aEvent, session);
 
 		var observer = b;
-		if (b.tabContainer && b.tabContainer._setEffectAllowedForDataTransfer)
+		if (
+			b.tabContainer &&
+			(
+				b.tabContainer._getDropEffectForTabDrag || // Firefox 44 and later
+				b.tabContainer._setEffectAllowedForDataTransfer // Firefox 43 and older
+			)
+			)
 			observer = b.tabContainer;
 
 		// auto-switch for staying on tabs
@@ -980,7 +986,9 @@ try{
 			) {
 			let time = observer.mDragTime || observer._dragTime || 0;
 			let delay = observer.mDragOverDelay || observer._dragOverDelay || 0;
-			let effects = observer._setEffectAllowedForDataTransfer(aEvent);
+			let effects = '_setEffectAllowedForDataTransfer' in observer ?
+							observer._setEffectAllowedForDataTransfer(aEvent) :
+							observer._getDropEffectForTabDrag(aEvent) ;
 			if (effects == 'link') {
 				let now = Date.now();
 				if (!time) {
@@ -995,14 +1003,20 @@ try{
 			}
 		}
 
+		{
+			let effects = '_setEffectAllowedForDataTransfer' in observer ?
+							observer._setEffectAllowedForDataTransfer(aEvent) :
+							observer._getDropEffectForTabDrag(aEvent) ;
+
 		if (
 			!info.canDrop ||
-			observer._setEffectAllowedForDataTransfer(aEvent) == 'none'
+			effects == 'none'
 			) {
 			aEvent.dataTransfer.effectAllowed = "none";
 			this.clearDropPosition();
 			return true;
 		}
+		}
 
 		let indicatorTab = info.target;
 		if (sv.isCollapsed(info.target)) {