diff --git a/_locales/de/messages.json b/_locales/de/messages.json
index 358036b..a976ef8 100644
--- a/_locales/de/messages.json
+++ b/_locales/de/messages.json
@@ -189,6 +189,43 @@
 		"description": ""
 	},
 	
+	"persistentRndClearInterval_title": {
+		"message": "Löschintervall der persistenten Daten",
+		"description": ""
+	},
+	"persistentRndClearInterval_description": {
+		"message": "Nach dem eingestellten Intervall werden die persistenten Daten automatisch gelöscht. (Null eingeben, um es zu deaktivieren.)",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.seconds": {
+		"message": "Sekunden",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.minutes": {
+		"message": "Minuten",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.hours": {
+		"message": "Stunden",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.days": {
+		"message": "Tage",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.weeks": {
+		"message": "Wochen",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.months": {
+		"message": "Monate",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.years": {
+		"message": "Jahre",
+		"description": ""
+	},
+	
 	"clearPersistentRnd_title": {
 		"message": "Persistenten Speicher leeren",
 		"description": ""
diff --git a/_locales/en/messages.json b/_locales/en/messages.json
index 5a71678..fb8e2a1 100644
--- a/_locales/en/messages.json
+++ b/_locales/en/messages.json
@@ -189,6 +189,43 @@
 		"description": ""
 	},
 	
+	"persistentRndClearInterval_title": {
+		"message": "Clear interval of the persistent data",
+		"description": ""
+	},
+	"persistentRndClearInterval_description": {
+		"message": "After the specified interval the persistent data is cleared automatically. (Enter zero to disable.)",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.seconds": {
+		"message": "seconds",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.minutes": {
+		"message": "minutes",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.hours": {
+		"message": "hours",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.days": {
+		"message": "days",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.weeks": {
+		"message": "weeks",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.months": {
+		"message": "months",
+		"description": ""
+	},
+	"persistentRndClearIntervalUnit_options.years": {
+		"message": "years",
+		"description": ""
+	},
+	
 	"clearPersistentRnd_title": {
 		"message": "Clear persistent random storage",
 		"description": ""
diff --git a/lib/logging.js b/lib/logging.js
index 7bfd49b..3d289ef 100644
--- a/lib/logging.js
+++ b/lib/logging.js
@@ -85,13 +85,13 @@
 			metaLog("logging queue cleared");
 		}
 	};
-	settings.on("isStillDefault", scope.clearQueue);
+	settings.loaded.then(scope.clearQueue);
 	scope.error = error;
 	scope.warning = warning;
 	scope.message = message;
 	scope.notice = notice;
 	scope.verbose = verbose;
-	
+
 	require.emit("./logging");
 
 	metaLog("logging available");
diff --git a/lib/main.js b/lib/main.js
index bba2533..c334b75 100644
--- a/lib/main.js
+++ b/lib/main.js
@@ -9,33 +9,13 @@
 	const {error, warning, message, notice, verbose, } = logging;
 	const lists = require("./lists");
 	logging.setPrefix("main script");
+	const persistentRndStorage = require("./persistentRndStorage");
 	
 	message("start of background script");
 	message("waiting for settings to be loaded");
 	settings.onloaded(function(){
 		notice("everything loaded");
 		
-		notice("build persistent storage");
-		var persistentRnd = Object.create(null);
-		try {
-			let storedData = JSON.parse(settings.persistentRndStorage);
-			for (var domain in storedData){
-				var value = storedData[domain];
-				if (
-					Array.isArray(value) &&
-					value.length === 128 &&
-					value.every(function(value){
-						return typeof value === "number" && value >= 0 && value < 256;
-					})
-				){
-					persistentRnd[domain] = value;
-				}
-			}
-		}
-		catch(e){
-			// JSON is not valid -> ignore it
-		}
-		
 		function updateContentScripts(){
 			message("update content scripts");
 			notice("build settings blob");
@@ -51,24 +31,26 @@
 			warning("TODO: register content scripts -> have to wait for the API to be released");
 		}
 		updateContentScripts();
+		persistentRndStorage.init();
 		
 		message("register non port message listener");
 		browser.runtime.onMessage.addListener(function(data){
 			notice("got data without port", data);
+			var keys = Object.keys(data);
 			if (data["canvasBlocker-new-domain-rnd"]){
-				verbose("got new domain rnd", data["canvasBlocker-new-domain-rnd"]);
-				data["canvasBlocker-set-domain-rnd"] = data["canvasBlocker-new-domain-rnd"];
-				persistentRnd[data["canvasBlocker-new-domain-rnd"].domain] = data["canvasBlocker-new-domain-rnd"].rnd;
-				if (settings.storePersistentRnd){
-					settings.persistentRndStorage = JSON.stringify(persistentRnd);
+				persistentRndStorage.setDomainData(
+					data["canvasBlocker-new-domain-rnd"].domain,
+					data["canvasBlocker-new-domain-rnd"].rnd
+				);
+				if (keys.length === 1){
+					return;
 				}
 				updateContentScripts();
 			}
 			if (data["canvasBlocker-clear-domain-rnd"]){
-				verbose("domain rnd cleared");
-				persistentRnd = Object.create(null);
-				if (settings.storePersistentRnd){
-					settings.persistentRndStorage = JSON.stringify(persistentRnd);
+				persistentRndStorage.clear();
+				if (keys.length === 1){
+					return;
 				}
 				updateContentScripts();
 			}
@@ -84,10 +66,10 @@
 		browser.runtime.onConnect.addListener(function(port){
 			notice("got port", port);
 			verbose("send back the tab id", port.sender.tab.id);
-			verbose("send back the persistent random seeds", persistentRnd);
+			verbose("send back the persistent random seeds", persistentRndStorage.persistentRnd);
 			port.postMessage({
 				tabId: port.sender.tab.id,
-				persistentRnd: persistentRnd
+				persistentRnd: persistentRndStorage.persistentRnd
 			});
 			var url = new URL(port.sender.url);
 			port.onMessage.addListener(function(data){
@@ -116,9 +98,6 @@
 				});
 			}
 		});
-		settings.on("storePersistentRnd", function({newValue}){
-			settings.persistentRndStorage = newValue? JSON.stringify(persistentRnd): "";
-		});
 		
 		// hide page action when a tab is refreshed
 		browser.tabs.onUpdated.addListener(function(tabId, data){
diff --git a/lib/persistentRndStorage.js b/lib/persistentRndStorage.js
new file mode 100644
index 0000000..758099c
--- /dev/null
+++ b/lib/persistentRndStorage.js
@@ -0,0 +1,111 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+(function(){
+	"use strict";
+
+	var scope;
+	if ((typeof exports) !== "undefined"){
+		scope = exports;
+	}
+	else {
+		scope = {};
+		window.scope.persistentRndStorage = scope;
+	}
+
+
+	const settings = require("./settings");
+	const logging = require("./logging");
+	
+	scope.persistentRnd = Object.create(null);
+	scope.init = function init(){
+		logging.message("initializing persistent rng storage");
+
+		logging.notice("build persistent storage");
+
+		if (settings.storePersistentRnd){
+			try {
+				let storedData = JSON.parse(settings.persistentRndStorage);
+				for (var domain in storedData){
+					var value = storedData[domain];
+					if (
+						Array.isArray(value) &&
+						value.length === 128 &&
+						value.every(function(value){
+							return typeof value === "number" && value >= 0 && value < 256;
+						})
+					){
+						scope.persistentRnd[domain] = value;
+					}
+				}
+			}
+			catch (e){
+				// JSON is not valid -> ignore it
+			}
+		}
+		else {
+			settings.persistentRndStorage = "";
+			settings.lastPersistentRndClearing = Date.now();
+		}
+
+		registerTimeout();
+
+		logging.notice("register settings change event listener");
+		settings.on(["persistentRndClearIntervalValue", "persistentRndClearIntervalUnit"], function(){
+			window.clearTimeout(clearTimeout);
+			registerTimeout();
+		});
+		settings.on("storePersistentRnd", function({newValue}){
+			settings.persistentRndStorage = newValue? JSON.stringify(scope.persistentRnd): "";
+		});
+	};
+
+	const getInterval = function(){
+		var units = {
+			seconds: 1000,
+			minutes: 60 * 1000,
+			hours: 60 * 60 * 1000,
+			days: 24 * 60 * 60 * 1000,
+			weeks: 7 * 24 * 60 * 60 * 1000,
+			months: 30 * 24 * 60 * 60 * 1000,
+			years: 365 * 24 * 60 * 60 * 1000,
+		};
+		return function getInterval(){
+			return settings.persistentRndClearIntervalValue * units[settings.persistentRndClearIntervalUnit] || 0;
+		};
+	}();
+
+	let clearTimeout;
+	function registerTimeout(){
+		var interval = getInterval();
+		if (interval > 0){
+			var timeout =  settings.lastPersistentRndClearing + interval - Date.now();
+			logging.message("registering persistent rng data clearing timeout. Clearing in ", timeout, "ms");
+			clearTimeout = window.setTimeout(clear, timeout);
+		}
+	}
+	function broadcast(data){
+		browser.tabs.query({}).then(function(tabs){
+			tabs.forEach(function(tab){
+				browser.tabs.sendMessage(tab.id, data);
+			});
+		});
+	}
+	function clear(){
+		logging.verbose("domain rnd cleared");
+		scope.persistentRnd = Object.create(null);
+		settings.persistentRndStorage = JSON.stringify(scope.persistentRnd);
+		settings.lastPersistentRndClearing = Date.now();
+		registerTimeout();
+		broadcast({"canvasBlocker-clear-domain-rnd": true});
+	}
+	function setDomainData(domain, rnd){
+		logging.verbose("got new domain rnd for ", domain, ":", rnd);
+		scope.persistentRnd[domain] = rnd;
+		settings.persistentRndStorage = JSON.stringify(scope.persistentRnd);
+		broadcast({"canvasBlocker-set-domain-rnd": {domain, rnd}});
+	}
+
+	scope.clear = clear;
+	scope.setDomainData = setDomainData;
+}());
\ No newline at end of file
diff --git a/lib/randomSupplies.js b/lib/randomSupplies.js
index dc53014..5e97656 100644
--- a/lib/randomSupplies.js
+++ b/lib/randomSupplies.js
@@ -12,6 +12,8 @@
 		window.scope.randomSupplies = {};
 		scope = window.scope.randomSupplies;
 	}
+
+	const settings = require("./settings");
 	
 	function getDomain(window){
 		if (!window.location.href || window.location.href === "about:blank"){
@@ -26,6 +28,26 @@
 	}
 
 	var persistentRnd = Object.create(null);
+	settings.onloaded(function(){
+		try {
+			let storedData = JSON.parse(settings.persistentRndStorage);
+			for (var domain in storedData){
+				var value = storedData[domain];
+				if (
+					Array.isArray(value) &&
+					value.length === 128 &&
+					value.every(function(value){
+						return typeof value === "number" && value >= 0 && value < 256;
+					})
+				){
+					persistentRnd[domain] = value;
+				}
+			}
+		}
+		catch (e){
+			// JSON is not valid -> ignore it
+		}
+	});
 	const getPersistentRnd = (function(){
 		
 		browser.runtime.onMessage.addListener(function(data){
diff --git a/lib/settingDefinitions.js b/lib/settingDefinitions.js
index c71d23b..87fae41 100644
--- a/lib/settingDefinitions.js
+++ b/lib/settingDefinitions.js
@@ -59,6 +59,19 @@
 			name: "storePersistentRnd",
 			defaultValue: false
 		},
+		{
+			name: "persistentRndClearIntervalValue",
+			defaultValue: 0
+		},
+		{
+			name: "persistentRndClearIntervalUnit",
+			defaultValue: "days",
+			options: ["seconds", "minutes", "hours", "days", "weeks", "months", "years"]
+		},
+		{
+			name: "lastPersistentRndClearing",
+			defaultValue: 0
+		},
 		{
 			name: "askOnlyOnce",
 			defaultValue: true
diff --git a/lib/settings.js b/lib/settings.js
index 725477b..d451fde 100644
--- a/lib/settings.js
+++ b/lib/settings.js
@@ -98,11 +98,18 @@
 		}).forEach(...args);
 	};
 	scope.on = function onSettingsChange(name, callback){
-		if (eventHandler.hasOwnProperty(name)){
-			eventHandler[name].push(callback);
+		if (Array.isArray(name)){
+			name.forEach(function(name){
+				onSettingsChange(name, callback);
+			});
 		}
 		else {
-			logging.warning("Unable to register event handler for unknown setting", name);
+			if (eventHandler.hasOwnProperty(name)){
+				eventHandler[name].push(callback);
+			}
+			else {
+				logging.warning("Unable to register event handler for unknown setting", name);
+			}
 		}
 	};
 
diff --git a/manifest.json b/manifest.json
index 048ef43..ce7f192 100644
--- a/manifest.json
+++ b/manifest.json
@@ -13,6 +13,7 @@
 			"lib/settings.js",
 			"lib/logging.js",
 			"lib/lists.js",
+			"lib/persistentRndStorage.js",
 			"lib/main.js"
 		]
 	},
diff --git a/options/options.css b/options/options.css
index 7c45cd6..edba211 100644
--- a/options/options.css
+++ b/options/options.css
@@ -25,4 +25,13 @@
 input[type=""], input[type="text"], input[type="number"], select {
 	width: 100%;
 	box-sizing: border-box;
+}
+*.multiple2 {
+	width: 50% !important;
+}
+*.multiple3 {
+	width: 33% !important;
+}
+*.multiple4 {
+	width: 25% !important;
 }
\ No newline at end of file
diff --git a/options/options.js b/options/options.js
index 87b4ec3..5f09ab6 100644
--- a/options/options.js
+++ b/options/options.js
@@ -31,7 +31,13 @@
 	settingsDisplay.forEach(function(display){
 		var setting = settings.getDefinition(display.name);
 		if (!setting){
-			if (callbacks[display.name]){
+			if (display.inputs){
+				setting = {
+					name: display.name,
+					inputs: display.inputs.map(settings.getDefinition)
+				};
+			}
+			else if (callbacks[display.name]){
 				setting = {
 					name: display.name,
 					action: callbacks[display.name]
diff --git a/options/optionsGui.js b/options/optionsGui.js
index 8787747..2eae93e 100644
--- a/options/optionsGui.js
+++ b/options/optionsGui.js
@@ -140,6 +140,14 @@
 		if (setting.action){
 			interaction = createButton(setting);
 		}
+		else if (setting.inputs){
+			interaction = document.createElement("span");
+			setting.inputs.forEach(function(inputSetting){
+				var input = createInput(inputSetting);
+				input.classList.add("multiple" + setting.inputs.length);
+				interaction.appendChild(input);
+			});
+		}
 		else {
 			interaction = createInput(setting);
 		}
diff --git a/options/settingsDisplay.js b/options/settingsDisplay.js
index 34c3ebf..ca83bde 100644
--- a/options/settingsDisplay.js
+++ b/options/settingsDisplay.js
@@ -51,6 +51,15 @@
 				"displayAdvancedSettings": [true]
 			}
 		},
+		{
+			"name": "persistentRndClearInterval",
+			"inputs": ["persistentRndClearIntervalValue", "persistentRndClearIntervalUnit"],
+			"displayDependencies": {
+				"blockMode": ["fakeReadout", "fakeInput"],
+				"rng": ["persistent"],
+				"displayAdvancedSettings": [true]
+			}
+		},
 		{
 			"name": "clearPersistentRnd",
 			"displayDependencies": {
diff --git a/releaseNotes.txt b/releaseNotes.txt
index 7dcfb9c..f954318 100644
--- a/releaseNotes.txt
+++ b/releaseNotes.txt
@@ -1,10 +1,11 @@
 Version 0.4.1:
 	changes:
 		- improved design of the page action display
-		- 
+		- Enabled Firefox ESR
+		- persistent random generator data is always stored in the settings but cleared on restart if the store flag is not set 
 	
 	new features:
-		- 
+		- setting to set an interval to clear the persistent random generator data
 	
 	fixes:
 		- unnecessary check for context type in getImageData broke websites