Noissue - Explicitly ignore asynchronous errors from tabs.insertCSS

lib/cssInjection.js

Index: lib/cssInjection.js
===================================================================
--- a/lib/cssInjection.js
+++ b/lib/cssInjection.js
@@ -71,23 +71,34 @@
   try
   {
     browser.tabs.insertCSS(tabId, {
       code: styleSheet,
       cssOrigin: "user",
       frameId,
       matchAboutBlank: true,
       runAt: "document_start"
-    });
+    })
+    // Some errors are asynchronous (e.g. frame-not-found on Chromium 66). We
+    // can simply ignore any such errors.
+    .catch(() => {});
   }
   catch (error)
   {
+    // If the error is about the "cssOrigin" option, this is an older version
+    // of Chromium (65 and below) or Firefox (52 and below) that does not
+    // support user style sheets.
     if (/\bcssOrigin\b/.test(error.message))
       userStyleSheetsSupported = false;
 
+    // Sometimes a frame gets removed from the document between the time the
+    // content script sends the "elemhide.getSelectors" message and the time
+    // the background page tries to inject a style sheet, which causes
+    // tabs.insertCSS to throw a frame-not-found error. We must handle any such
+    // errors.
     return false;
   }
 
   return true;
 }
 
 function removeStyleSheet(tabId, frameId, styleSheet)
 {