--- a/toolkit/content/browser-child.js
+++ b/toolkit/content/browser-child.js
@@ -554,19 +554,21 @@ addMessageListener("Browser:Thumbnail:Re
     });
   });
 });
 
 /**
  * Remote isSafeForCapture request handler for PageThumbs.
  */
 addMessageListener("Browser:Thumbnail:CheckState", function(aMessage) {
-  let result = PageThumbUtils.shouldStoreContentThumbnail(content, docShell);
-  sendAsyncMessage("Browser:Thumbnail:CheckState:Response", {
-    result
+  Services.tm.idleDispatchToMainThread(() => {
+    let result = PageThumbUtils.shouldStoreContentThumbnail(content, docShell);
+    sendAsyncMessage("Browser:Thumbnail:CheckState:Response", {
+      result
+    });
   });
 });
 
 /**
  * Remote GetOriginalURL request handler for PageThumbs.
  */
 addMessageListener("Browser:Thumbnail:GetOriginalURL", function(aMessage) {
   let channel = docShell.currentDocumentChannel;