diff --git a/platform/chromium/vapi-background.js b/platform/chromium/vapi-background.js
index 4ba0a1595..12be4a9d9 100644
--- a/platform/chromium/vapi-background.js
+++ b/platform/chromium/vapi-background.js
@@ -49,6 +49,12 @@ vAPI.resetLastError = function() {
 };
 
 vAPI.supportsUserStylesheets = vAPI.webextFlavor.soup.has('user_stylesheet');
+// The real actual webextFlavor value may not be set in stone, so listen
+// for possible future changes.
+window.addEventListener('webextFlavor', function() {
+    vAPI.supportsUserStylesheets =
+        vAPI.webextFlavor.soup.has('user_stylesheet');
+}, { once: true });
 
 vAPI.insertCSS = function(tabId, details) {
     return chrome.tabs.insertCSS(tabId, details, vAPI.resetLastError);
@@ -721,8 +727,7 @@ vAPI.messaging.listen = function(listenerName, callback) {
 /******************************************************************************/
 
 vAPI.messaging.onPortMessage = (function() {
-    var messaging = vAPI.messaging,
-        supportsUserStylesheets = vAPI.supportsUserStylesheets;
+    var messaging = vAPI.messaging;
 
     // Use a wrapper to avoid closure and to allow reuse.
     var CallbackWrapper = function(port, request) {
@@ -806,7 +811,7 @@ vAPI.messaging.onPortMessage = (function() {
                 frameId: sender.frameId,
                 matchAboutBlank: true
             };
-            if ( supportsUserStylesheets ) {
+            if ( vAPI.supportsUserStylesheets ) {
                 details.cssOrigin = 'user';
             }
             if ( msg.add ) {
diff --git a/platform/chromium/vapi-common.js b/platform/chromium/vapi-common.js
index 57a9a5b9b..19f465963 100644
--- a/platform/chromium/vapi-common.js
+++ b/platform/chromium/vapi-common.js
@@ -69,7 +69,9 @@ vAPI.webextFlavor = {
             flavor.major = parseInt(info.version, 10) || 0;
             soup.add(info.vendor.toLowerCase())
                 .add(info.name.toLowerCase());
+            soup.delete('user_stylesheet');
             if ( flavor.major >= 53 ) { soup.add('user_stylesheet'); }
+            soup.delete('html_filtering');
             if ( flavor.major >= 57 ) { soup.add('html_filtering'); }
             dispatch();
         });
diff --git a/src/js/cosmetic-filtering.js b/src/js/cosmetic-filtering.js
index a5590b00d..cf8dee775 100644
--- a/src/js/cosmetic-filtering.js
+++ b/src/js/cosmetic-filtering.js
@@ -543,6 +543,11 @@ FilterContainer.prototype.freeze = function() {
     this.highlyGeneric.simple.str = µb.arrayFrom(this.highlyGeneric.simple.dict).join(',\n');
     this.highlyGeneric.complex.str = µb.arrayFrom(this.highlyGeneric.complex.dict).join(',\n');
 
+    // https://www.reddit.com/r/uBlockOrigin/comments/8dkvqn/116_broken_loading_custom_filters_from_my_filters/
+    //   Just in case. This can be removed once Firefox 60 ESR is out
+    //   and widespread.
+    this.supportsUserStylesheets = vAPI.supportsUserStylesheets;
+
     this.frozen = true;
 };