diff --git a/platform/webext/vapi-webrequest.js b/platform/webext/vapi-webrequest.js
index a5638ce39..7945bd485 100644
--- a/platform/webext/vapi-webrequest.js
+++ b/platform/webext/vapi-webrequest.js
@@ -32,7 +32,7 @@ vAPI.net.registerListeners = function() {
     // https://github.com/gorhill/uBlock/issues/2950
     // Firefox 55 does not normalize URLs to ASCII, uBO must do this itself.
     // https://bugzilla.mozilla.org/show_bug.cgi?id=945240
-    var belowFirefox56 = false;
+    var mustPunycode = false;
     (function() {
         if ( 
             typeof browser === 'object' &&
@@ -41,8 +41,8 @@ vAPI.net.registerListeners = function() {
             typeof browser.runtime.getBrowserInfo === 'function'
         ) {
             browser.runtime.getBrowserInfo().then(info => {
-                belowFirefox56 = info.name === 'Firefox' &&
-                                 /^5[0-5]\./.test(info.version);
+                mustPunycode = info.name === 'Firefox' &&
+                               /^5[0-6]\./.test(info.version);
             });
         }
     })();
@@ -100,7 +100,7 @@ vAPI.net.registerListeners = function() {
         details.tabId = details.tabId.toString();
 
         if (
-            belowFirefox56 === true &&
+            mustPunycode === true &&
             reMustNormalizeHostname.test(details.url) === true
         ) {
             parsedURL.href = details.url;