From 832ebd360e52086badc29f8fe160b8b047ccf2f1 Mon Sep 17 00:00:00 2001
From: Raymond Hill <rhill@raymondhill.net>
Date: Sun, 8 Dec 2019 11:08:04 -0500
Subject: [PATCH] Mind that Firefox 59 and less does not support `browser.dns`

---
 platform/firefox/vapi-webrequest.js | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/platform/firefox/vapi-webrequest.js b/platform/firefox/vapi-webrequest.js
index d077da1bd..8b182f883 100644
--- a/platform/firefox/vapi-webrequest.js
+++ b/platform/firefox/vapi-webrequest.js
@@ -68,11 +68,12 @@
             this.cnameMaxTTL = 60;
             this.cnameReplayFullURL = false;
             this.cnameTimer = undefined;
-            this.cnameUncloak = true;
+            this.cnameUncloak = browser.dns instanceof Object;
         }
         setOptions(options) {
             super.setOptions(options);
-            this.cnameUncloak = options.cnameUncloak !== false;
+            this.cnameUncloak = browser.dns instanceof Object &&
+                                options.cnameUncloak !== false;
             this.cnameIgnoreList = this.regexFromStrList(options.cnameIgnoreList);
             this.cnameIgnore1stParty = options.cnameIgnore1stParty !== false;
             this.cnameIgnoreExceptions = options.cnameIgnoreExceptions !== false;
@@ -202,6 +203,7 @@
         }
         onBeforeSuspendableRequest(details) {
             const r = super.onBeforeSuspendableRequest(details);
+            if ( this.cnameUncloak === false ) { return r; }
             if ( r !== undefined ) {
                 if (
                     r.cancel === true ||
@@ -217,7 +219,6 @@
             ) {
                 return;
             }
-            if ( this.cnameUncloak === false ) { return; }
             const hn = vAPI.hostnameFromNetworkURL(details.url);
             const cname = this.cnames.get(hn);
             if ( cname === '' ) { return; }