diff --git a/content/treestyletab/config.js b/content/treestyletab/config.js
index 29f77b15..ab3840e5 100644
--- a/content/treestyletab/config.js
+++ b/content/treestyletab/config.js
@@ -195,7 +195,7 @@ function onSyncGroupBookmarkPrefToUI()
 }
 
 
-function onChangeTabbarPosition(aOnChange)
+function onChangeTabbarPosition()
 {
 	var pos = document.getElementById('extensions.treestyletab.tabbar.position-radiogroup').value;
 	var invertTab = document.getElementById('extensions.treestyletab.tabbar.invertTab-check');
@@ -216,24 +216,24 @@ function onChangeTabbarPosition(aOnChange)
 	else
 		invertClosebox.setAttribute('collapsed', true);
 
-	var indentCheckH   = document.getElementById('extensions.treestyletab.enableSubtreeIndent.horizontal-check');
-	var indentCheckV   = document.getElementById('extensions.treestyletab.enableSubtreeIndent.vertical-check');
+	var maxTreeLevelH   = document.getElementById('maxTreeLevel-groupbox-horizontal');
+	var maxTreeLevelV   = document.getElementById('maxTreeLevel-groupbox-vertical');
 	var collapseCheckH = document.getElementById('extensions.treestyletab.allowSubtreeCollapseExpand.horizontal-check');
 	var collapseCheckV = document.getElementById('extensions.treestyletab.allowSubtreeCollapseExpand.vertical-check');
 	var hideAllTabsCheckH = document.getElementById('extensions.treestyletab.tabbar.hideAlltabsButton.horizontal-check');
 	var hideAllTabsCheckV = document.getElementById('extensions.treestyletab.tabbar.hideAlltabsButton.vertical-check');
 
 	if (pos == 'left' || pos == 'right') {
-		indentCheckH.setAttribute('collapsed', true);
-		indentCheckV.removeAttribute('collapsed');
+		maxTreeLevelH.setAttribute('collapsed', true);
+		maxTreeLevelV.removeAttribute('collapsed');
 		collapseCheckH.setAttribute('collapsed', true);
 		collapseCheckV.removeAttribute('collapsed');
 		hideAllTabsCheckH.setAttribute('collapsed', true);
 		hideAllTabsCheckV.removeAttribute('collapsed');
 	}       
 	else {
-		indentCheckH.removeAttribute('collapsed');
-		indentCheckV.setAttribute('collapsed', true);
+		maxTreeLevelH.removeAttribute('collapsed');
+		maxTreeLevelV.setAttribute('collapsed', true);
 		collapseCheckH.removeAttribute('collapsed');
 		collapseCheckV.setAttribute('collapsed', true);
 		hideAllTabsCheckH.removeAttribute('collapsed');
@@ -243,6 +243,52 @@ function onChangeTabbarPosition(aOnChange)
 	gTabbarPlacePositionInitialized = true;
 }
 
+function onSyncMaxTreeLevelUIToPref(aTarget)
+{
+	var isHorizontal = aTarget.indexOf('horizontal') != -1;
+	aTarget = document.getElementById(aTarget);
+	if (aTarget.sync)
+		return;
+	aTarget.sync = true;
+
+	var UIValue = parseInt(aTarget.value);
+	var prefValue = UIValue;
+	Array.slice(aTarget.getElementsByTagName('textbox')).forEach(function(aNode) {
+		if (aNode.getAttribute('max-tree-level-radio') == UIValue) {
+			aNode.removeAttribute('disabled');
+			prefValue = parseInt(aNode.value);
+		}
+		else
+			aNode.setAttribute('disabled', true);
+	});
+	aTarget.sync = false;
+	return prefValue;
+}
+
+function onSyncMaxTreeLevelPrefToUI(aTarget)
+{
+	var isHorizontal = aTarget.indexOf('horizontal') != -1;
+	aTarget = document.getElementById(aTarget);
+	if (aTarget.sync)
+		return;
+	aTarget.sync = true;
+
+	var pref = document.getElementById(aTarget.getAttribute('preference'));
+	var value = pref.value;
+
+	var UIValue = Math.max(-1, Math.min(1, value));
+	Array.slice(aTarget.getElementsByTagName('textbox')).forEach(function(aNode) {
+		if (aNode.getAttribute('max-tree-level-radio') == UIValue) {
+			aNode.removeAttribute('disabled');
+			aNode.value = value;
+		}
+		else
+			aNode.setAttribute('disabled', true);
+	});
+	aTarget.sync = false;
+	return UIValue;
+}
+
 
 var gAutoHideModeRadio,
 	gAutoHideModeToggle,
diff --git a/content/treestyletab/config.xul b/content/treestyletab/config.xul
index ec12dd4f..f8572a35 100644
--- a/content/treestyletab/config.xul
+++ b/content/treestyletab/config.xul
@@ -24,12 +24,12 @@
 		<preference id="extensions.treestyletab.tabbar.syncRelatedPrefsForDynamicPosition"
 			name="extensions.treestyletab.tabbar.syncRelatedPrefsForDynamicPosition"
 			type="bool"/>
-		<preference id="extensions.treestyletab.enableSubtreeIndent.horizontal"
-			name="extensions.treestyletab.enableSubtreeIndent.horizontal"
-			type="bool"/>
-		<preference id="extensions.treestyletab.enableSubtreeIndent.vertical"
-			name="extensions.treestyletab.enableSubtreeIndent.vertical"
-			type="bool"/>
+		<preference id="extensions.treestyletab.maxTreeLevel.horizontal"
+			name="extensions.treestyletab.maxTreeLevel.horizontal"
+			type="int"/>
+		<preference id="extensions.treestyletab.maxTreeLevel.vertical"
+			name="extensions.treestyletab.maxTreeLevel.vertical"
+			type="int"/>
 		<preference id="extensions.treestyletab.allowSubtreeCollapseExpand.horizontal"
 			name="extensions.treestyletab.allowSubtreeCollapseExpand.horizontal"
 			type="bool"/>
@@ -121,26 +121,68 @@
 			<checkbox id="extensions.treestyletab.allowSubtreeCollapseExpand.vertical-check"
 				preference="extensions.treestyletab.allowSubtreeCollapseExpand.vertical"
 				label="&config.allowSubtreeCollapseExpand;"/>
-			<checkbox id="extensions.treestyletab.enableSubtreeIndent.horizontal-check"
-				preference="extensions.treestyletab.enableSubtreeIndent.horizontal"
-				label="&config.enableSubtreeIndent;"
-				oncommand="
-					if (document.getElementById('extensions.treestyletab.tabbar.syncRelatedPrefsForDynamicPosition').value)
-						document.getElementById('extensions.treestyletab.tabbar.fixed.horizontal').value = !this.checked;
-				"/>
-			<checkbox id="extensions.treestyletab.enableSubtreeIndent.vertical-check"
-				preference="extensions.treestyletab.enableSubtreeIndent.vertical"
-				label="&config.enableSubtreeIndent;"/>
-		</hbox>
-		<hbox align="center" id="hideAlltabsButton-box">
-			<checkbox id="extensions.treestyletab.tabbar.hideAlltabsButton.horizontal-check"
-				preference="extensions.treestyletab.tabbar.hideAlltabsButton.horizontal"
-				label="&config.tabbar.hideAlltabsButton;"
-				collapsed="true"/>
-			<checkbox id="extensions.treestyletab.tabbar.hideAlltabsButton.vertical-check"
-				preference="extensions.treestyletab.tabbar.hideAlltabsButton.vertical"
-				label="&config.tabbar.hideAlltabsButton;"/>
+			<hbox align="center" id="hideAlltabsButton-box">
+				<checkbox id="extensions.treestyletab.tabbar.hideAlltabsButton.horizontal-check"
+					preference="extensions.treestyletab.tabbar.hideAlltabsButton.horizontal"
+					label="&config.tabbar.hideAlltabsButton;"
+					collapsed="true"/>
+				<checkbox id="extensions.treestyletab.tabbar.hideAlltabsButton.vertical-check"
+					preference="extensions.treestyletab.tabbar.hideAlltabsButton.vertical"
+					label="&config.tabbar.hideAlltabsButton;"/>
+			</hbox>
 		</hbox>
+		<groupbox id="maxTreeLevel-groupbox-vertical">
+			<caption label="&config.maxTreeLevel.caption;"/>
+			<radiogroup id="maxTreeLevel-radiogroup-vertical"
+				orient="vertical"
+				preference="extensions.treestyletab.maxTreeLevel.vertical"
+				onsynctopreference="return onSyncMaxTreeLevelUIToPref('maxTreeLevel-radiogroup-vertical');"
+				onsyncfrompreference="return onSyncMaxTreeLevelPrefToUI('maxTreeLevel-radiogroup-vertical');">
+				<radio value="0"  label="&config.maxTreeLevel.0;"
+					max-tree-level-radio="0"/>
+				<radio value="-1" label="&config.maxTreeLevel.-1;"
+					max-tree-level-radio="-1"/>
+				<hbox align="center">
+					<radio value="1" id="maxTreeLevel-radio1-vertical"
+						max-tree-level-radio="1"
+						label="&config.maxTreeLevel.1;"/>
+					<textbox id="maxTreeLevel-radio1-textbox-vertical"
+						max-tree-level-radio="1"
+						type="number"
+						min="1" increment="1" size="2"
+						oninput="document.getElementById(this.parentNode.parentNode.getAttribute('preference')).value = this.value;"/>
+					<label max-tree-level-radio="1"
+						control="maxTreeLevel-radio1-vertical"
+						value="&config.maxTreeLevel.1.after;"/>
+				</hbox>
+			</radiogroup>
+		</groupbox>
+		<groupbox id="maxTreeLevel-groupbox-horizontal" collapsed="true">
+			<caption label="&config.maxTreeLevel.caption;"/>
+			<radiogroup id="maxTreeLevel-radiogroup-horizontal"
+				orient="vertical"
+				preference="extensions.treestyletab.maxTreeLevel.horizontal"
+				onsynctopreference="return onSyncMaxTreeLevelUIToPref('maxTreeLevel-radiogroup-horizontal');"
+				onsyncfrompreference="return onSyncMaxTreeLevelPrefToUI('maxTreeLevel-radiogroup-horizontal');">
+				<radio value="0"  label="&config.maxTreeLevel.0;"
+					max-tree-level-radio="0"/>
+				<radio value="-1" label="&config.maxTreeLevel.-1;"
+					max-tree-level-radio="-1"/>
+				<hbox align="center">
+					<radio value="1" id="maxTreeLevel-radio1-horizontal"
+						max-tree-level-radio="1"
+						label="&config.maxTreeLevel.1;"/>
+					<textbox id="maxTreeLevel-radio1-textbox-horizontal"
+						max-tree-level-radio="1"
+						type="number"
+						min="1" increment="1" size="2"
+						oninput="document.getElementById(this.parentNode.parentNode.getAttribute('preference')).value = this.value;"/>
+					<label max-tree-level-radio="1"
+						control="maxTreeLevel-radio1-horizontal"
+						value="&config.maxTreeLevel.1.after;"/>
+				</hbox>
+			</radiogroup>
+		</groupbox>
 		</vbox>
 	</groupbox>
 
@@ -236,6 +278,9 @@
 		<preference id="extensions.treestyletab.show.context-item-bookmarkTabSubtree"
 			name="extensions.treestyletab.show.context-item-bookmarkTabSubtree"
 			type="bool"/>
+		<preference id="extensions.treestyletab.preferences.newTab-tabbox.selectedIndex"
+			name="extensions.treestyletab.preferences.newTab-tabbox.selectedIndex"
+			type="int"/>
 	</preferences>
 
 	<vbox>
diff --git a/locale/en-US/treestyletab/treestyletab.dtd b/locale/en-US/treestyletab/treestyletab.dtd
index c9a90847..4bf3ec7c 100644
--- a/locale/en-US/treestyletab/treestyletab.dtd
+++ b/locale/en-US/treestyletab/treestyletab.dtd
@@ -15,7 +15,11 @@
 <!ENTITY config.tabbar.invertClosebox.right "Show closebox at rightside in each tab">
 <!ENTITY config.tabbar.invertTab            "Invert tab appearance">
 <!ENTITY config.tabbar.invertTabContents    "Invert tab contents">
-<!ENTITY config.enableSubtreeIndent         "Indent tabs">
+<!ENTITY config.maxTreeLevel.caption  "Visualization of nested trees">
+<!ENTITY config.maxTreeLevel.0        "Nothing (no indentation)">
+<!ENTITY config.maxTreeLevel.-1       "Indent tabs">
+<!ENTITY config.maxTreeLevel.1        "Indent tabs until">
+<!ENTITY config.maxTreeLevel.1.after  "level(s)">
 <!ENTITY config.allowSubtreeCollapseExpand  "Allow to collapse/expand tree of tabs">
 <!ENTITY config.tabbar.hideAlltabsButton    "Show &quot;List all tabs&quot; button">
 
diff --git a/locale/ja/treestyletab/treestyletab.dtd b/locale/ja/treestyletab/treestyletab.dtd
index f60a803f..9b080001 100644
--- a/locale/ja/treestyletab/treestyletab.dtd
+++ b/locale/ja/treestyletab/treestyletab.dtd
@@ -15,7 +15,11 @@
 <!ENTITY config.tabbar.invertClosebox.right "タブのクローズボックスを右に表示">
 <!ENTITY config.tabbar.invertTab            "タブの表示を左右反転">
 <!ENTITY config.tabbar.invertTabContents    "タブの内容を左右反転">
-<!ENTITY config.enableSubtreeIndent         "タブをインデント表示する">
+<!ENTITY config.maxTreeLevel.caption  "ツリーの深さの表示">
+<!ENTITY config.maxTreeLevel.0        "何もしない（インデントなし）">
+<!ENTITY config.maxTreeLevel.-1       "タブをインデント表示する">
+<!ENTITY config.maxTreeLevel.1        "タブをインデント表示する（">
+<!ENTITY config.maxTreeLevel.1.after  "階層まで）">
 <!ENTITY config.allowSubtreeCollapseExpand  "ツリーを折りたためるようにする">
 <!ENTITY config.tabbar.hideAlltabsButton    "「タブの一覧を表示」ボタンを表示する">