This addresses Opera seemingly not supporting managed storage.

As reported in 43a5ed735b (all_commit_comments)

platform/chromium/vapi-background.js

@@ -37,6 +37,7 @@ var chrome = self.chrome;
 var manifest = chrome.runtime.getManifest();
 
 vAPI.chrome = true;
+vAPI.opera = /\bOPR\/[\d.]+\b/.test(self.navigator.appVersion);
 
 var noopFunc = function(){};
 
@@ -1011,12 +1012,29 @@ vAPI.punycodeURL = function(url) {
 // https://github.com/gorhill/uBlock/issues/531
 // Storage area dedicated to admin settings. Read-only.
 
+// https://github.com/gorhill/uBlock/commit/43a5ed735b95a575a9339b6e71a1fcb27a99663b#commitcomment-13965030
+// Not all Chromium-based browsers support managed storage. Merely testing or
+// exception handling in this case does NOT work: I don't why. The extension
+// on Opera ends up in a non-sensical state, whereas vAPI become undefined out
+// of nowhere. So only solution left is to test explicitly for Opera.
+
 vAPI.adminStorage = {
-    getItem: function(key, callback) {
+    getItem: (function() {
+        if ( vAPI.opera ) {
+            return function(key, callback) {
+                callback();
+            };
+        }
+        return function(key, callback) {
+            try {
                 chrome.storage.managed.get(key, function(store) {
                     callback(store[key] || undefined);
                 });
+            } catch (ex) {
+                callback();
             }
+        };
+    })()
 };
 
 /******************************************************************************/