Issue 5769 - Worked around bad Firefox 55 storage performance

lib/prefs.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 220 matching lines @@
     return null;
 
   return key.substr(keyPrefix.length);
 }
 
 function prefToKey(pref)
 {
   return keyPrefix + pref;
 }
 
+function savePref(pref)
+{
+  ext.storage.set(prefToKey(pref), overrides[pref]);
+}
+
+let customSave = new Map();
+if (require("info").platform == "gecko")
+{
+  // Saving one storage value causes all others to be saved as well on Gecko.
+  // Make sure that updating ad counter doesn't cause the filters data to be
+  // saved frequently as a side-effect.
+  const MIN_UPDATE_INTERVAL = 60 * 1000;
+  let lastUpdate = -MIN_UPDATE_INTERVAL;
+  let updateScheduled = false;
+  customSave.set("blocked_total", pref =>
+  {
+    if (updateScheduled)
+      return;
+
+    let callback = () =>
+    {
+      lastUpdate = performance.now();
+      updateScheduled = false;
+      savePref(pref);
+    };
+
+    let timeElapsed = performance.now() - lastUpdate;
+    if (timeElapsed < MIN_UPDATE_INTERVAL)
+    {
+      setTimeout(callback, MIN_UPDATE_INTERVAL - timeElapsed);
+      updateScheduled = true;
+    }
+    else
+      callback();
+  });
+}
+
 function addPreference(pref)
 {
   Object.defineProperty(Prefs, pref, {
     get() { return (pref in overrides ? overrides : defaults)[pref]; },
     set(value)
     {
       let defaultValue = defaults[pref];
 
       if (typeof value != typeof defaultValue)
         throw new Error("Attempt to change preference type");
 
       if (value == defaultValue)
       {
         delete overrides[pref];
         ext.storage.remove(prefToKey(pref));
       }
       else
       {
         overrides[pref] = value;
-        ext.storage.set(prefToKey(pref), value);
+        (customSave.get(pref) || savePref)(pref);
       }
     },
     enumerable: true
   });
 }
 
 function init()
 {
   let prefs = Object.keys(defaults);
   prefs.forEach(addPreference);
@@ skipping 51 matching lines @@
           eventEmitter.emit(pref);
         }
       }
     });
   }
 
   Prefs.untilLoaded = Promise.all([localLoaded, managedLoaded]).then(onLoaded);
 }
 
 init();