diff --git a/background/db-chrome-storage.js b/background/db-chrome-storage.js
new file mode 100644
index 00000000..46cfadb1
--- /dev/null
+++ b/background/db-chrome-storage.js
@@ -0,0 +1,84 @@
+/* global promisify */
+/* exported createChromeStorageDB */
+'use strict';
+
+function createChromeStorageDB() {
+  const get = promisify(chrome.storage.local.get.bind(chrome.storage.local));
+  const set = promisify(chrome.storage.local.set.bind(chrome.storage.local));
+  const remove = promisify(chrome.storage.local.remove.bind(chrome.storage.local));
+
+  let INC;
+
+  const PREFIX = 'style-';
+  const METHODS = {
+    // FIXME: we don't use this method at all. Should we remove this?
+    get: id => get(PREFIX + id)
+      .then(result => result[PREFIX + id]),
+    put: obj => Promise.resolve()
+      .then(() => {
+        if (!obj.id) {
+          return prepareInc()
+            .then(() => {
+              // FIXME: should we clone the object?
+              obj.id = INC++;
+            });
+        }
+      })
+      .then(() => set({[PREFIX + obj.id]: obj}))
+      .then(() => obj.id),
+    putMany: items => prepareInc()
+      .then(() => {
+        for (const item of items) {
+          if (!item.id) {
+            item.id = INC++;
+          }
+        }
+        return set(items.reduce((obj, curr) => {
+          obj[PREFIX + curr.id] = curr;
+          return obj;
+        }, {}));
+      })
+      .then(() => items.map(i => i.id)),
+    delete: id => remove(PREFIX + id),
+    getAll: () => get(null)
+      .then(result => {
+        const output = [];
+        for (const key in result) {
+          if (key.startsWith(PREFIX) && Number(key.slice(PREFIX.length))) {
+            output.push(result[key]);
+          }
+        }
+        return output;
+      })
+  };
+
+  return {exec};
+
+  function exec(method, ...args) {
+    if (METHODS[method]) {
+      return METHODS[method](...args)
+        .then(result => {
+          if (method === 'putMany' && result.map) {
+            return result.map(r => ({target: {result: r}}));
+          }
+          return {target: {result}};
+        });
+    }
+    return Promise.reject(new Error(`unknown DB method ${method}`));
+  }
+
+  function prepareInc() {
+    if (INC) return Promise.resolve();
+    return get(null).then(result => {
+      INC = 1;
+      for (const key in result) {
+        if (key.startsWith(PREFIX)) {
+          const id = Number(key.slice(PREFIX.length));
+          if (id >= INC) {
+            INC = id + 1;
+          }
+        }
+      }
+    });
+  }
+}
diff --git a/background/db.js b/background/db.js
index 46fd0c9b..2549a3ce 100644
--- a/background/db.js
+++ b/background/db.js
@@ -1,4 +1,4 @@
-/* global chromeLocal ignoreChromeError workerUtil */
+/* global chromeLocal ignoreChromeError workerUtil createChromeStorageDB */
 /* exported db */
 /*
 Initialize a database. There are some problems using IndexedDB in Firefox:
@@ -94,7 +94,7 @@ const db = (() => {
   }
 
   function useChromeStorage(err) {
-    exec = dbExecChromeStorage;
+    exec = createChromeStorageDB().exec;
     chromeLocal.set({dbInChromeStorage: true}, ignoreChromeError);
     if (err) {
       chromeLocal.setValue('dbInChromeStorageReason', workerUtil.cloneError(err));
@@ -153,75 +153,4 @@ const db = (() => {
       return Promise.all(items.map(item => storeRequest(store, 'put', item)));
     }
   }
-
-  function dbExecChromeStorage(method, data) {
-    const STYLE_KEY_PREFIX = 'style-';
-    switch (method) {
-      case 'get':
-        return chromeLocal.getValue(STYLE_KEY_PREFIX + data)
-          .then(result => ({target: {result}}));
-
-      case 'put':
-        if (!data.id) {
-          return getMaxId().then(id => {
-            data.id = id + 1;
-            return dbExecChromeStorage('put', data);
-          });
-        }
-        return chromeLocal.setValue(STYLE_KEY_PREFIX + data.id, data)
-          .then(() => (chrome.runtime.lastError ? Promise.reject() : data.id));
-
-      case 'putMany': {
-        const newItems = data.filter(i => !i.id);
-        const doPut = () =>
-          chromeLocal.set(data.reduce((o, item) => {
-            o[STYLE_KEY_PREFIX + item.id] = item;
-            return o;
-          }, {}))
-            .then(() => data.map(d => ({target: {result: d.id}})));
-        if (newItems.length) {
-          return getMaxId().then(id => {
-            for (const item of newItems) {
-              item.id = ++id;
-            }
-            return doPut();
-          });
-        }
-        return doPut();
-      }
-
-      case 'delete':
-        return chromeLocal.remove(STYLE_KEY_PREFIX + data);
-
-      case 'getAll':
-        return getAllStyles()
-          .then(styles => ({target: {result: styles}}));
-    }
-    return Promise.reject();
-
-    function getAllStyles() {
-      return chromeLocal.get(null).then(storage => {
-        const styles = [];
-        for (const key in storage) {
-          if (key.startsWith(STYLE_KEY_PREFIX) &&
-              Number(key.substr(STYLE_KEY_PREFIX.length))) {
-            styles.push(storage[key]);
-          }
-        }
-        return styles;
-      });
-    }
-
-    function getMaxId() {
-      return getAllStyles().then(styles => {
-        let result = 0;
-        for (const style of styles) {
-          if (style.id > result) {
-            result = style.id;
-          }
-        }
-        return result;
-      });
-    }
-  }
 })();
diff --git a/manifest.json b/manifest.json
index c250caf1..fc7e94a6 100644
--- a/manifest.json
+++ b/manifest.json
@@ -41,6 +41,7 @@
       "background/token-manager.js",
       "background/sync.js",
       "background/content-scripts.js",
+      "background/db-chrome-storage.js",
       "background/db.js",
       "background/style-manager.js",
       "background/navigator-util.js",