diff --git a/src/vs/workbench/browser/parts/editor/iframeEditor.ts b/src/vs/workbench/browser/parts/editor/iframeEditor.ts
index 607601ae9d03272852199480cd555b0e780c0b7e..61bdf5690909970efc240ab0bdb4967d36c53e30 100644
--- a/src/vs/workbench/browser/parts/editor/iframeEditor.ts
+++ b/src/vs/workbench/browser/parts/editor/iframeEditor.ts
@@ -197,7 +197,11 @@ export class IFrameEditor extends BaseEditor {
 			'window.document.body.addEventListener("drop", function (e) {',
 			'	e.preventDefault();',
 			'});',
-			'</script>'
+
+			// disable navigating to some URL!
+			'window.onbeforeunload = function () {',
+			'	return false;',
+			'};'
 		].join('\n');
 	}
 
@@ -210,7 +214,7 @@ export class IFrameEditor extends BaseEditor {
 	}
 
 	private clearIFrame(): void {
-		this.iframeBuilder.src('about:blank');
+		this.setFrameContents(null, '', true);
 		this.iframeBuilder.removeProperty(IFrameEditor.RESOURCE_PROPERTY);
 	}
 
diff --git a/src/vs/workbench/parts/html/browser/htmlPreviewPart.ts b/src/vs/workbench/parts/html/browser/htmlPreviewPart.ts
index 598b7a2d85ad6ca851b5d4425881de18d46fee13..33161a50f3303180e3a2e00b740733c9135d043d 100644
--- a/src/vs/workbench/parts/html/browser/htmlPreviewPart.ts
+++ b/src/vs/workbench/parts/html/browser/htmlPreviewPart.ts
@@ -262,7 +262,12 @@ namespace Integration {
 		'});',
 		'window.document.body.addEventListener("drop", function (e) {',
 		'	e.preventDefault();',
-		'});'
+		'});',
+
+		// disable navigating to some URL!
+		'window.onbeforeunload = function () {',
+		'	return false;',
+		'};'
 	];
 
 	export function defaultHtml() {