diff --git a/src/background/actions/command.js b/src/background/actions/command.js
index f1ee5b5..a6e426a 100644
--- a/src/background/actions/command.js
+++ b/src/background/actions/command.js
@@ -5,56 +5,63 @@ import * as bookmarks from '../shared/bookmarks';
 import * as parsers from 'shared/commands/parsers';
 import * as properties from 'shared/settings/properties';
 
-const openCommand = (url) => {
-  return browser.tabs.query({
+const openCommand = async(url) => {
+  let got = await browser.tabs.query({
     active: true, currentWindow: true
-  }).then((gotTabs) => {
-    if (gotTabs.length > 0) {
-      return browser.tabs.update(gotTabs[0].id, { url: url });
-    }
   });
+  if (got.length > 0) {
+    return browser.tabs.update(got[0].id, { url: url });
+  }
 };
 
 const tabopenCommand = (url) => {
   return browser.tabs.create({ url: url });
 };
 
-const tabcloseCommand = () => {
-  return browser.tabs.query({
+const tabcloseCommand = async() => {
+  let got = await browser.tabs.query({
     active: true, currentWindow: true
-  }).then((tabList) => {
-    return browser.tabs.remove(tabList.map(tab => tab.id));
   });
+  return browser.tabs.remove(got.map(tab => tab.id));
 };
 
 const winopenCommand = (url) => {
   return browser.windows.create({ url });
 };
 
-const bufferCommand = (keywords) => {
+const bufferCommand = async(keywords) => {
   if (keywords.length === 0) {
     return Promise.resolve([]);
   }
   let keywordsStr = keywords.join(' ');
-  return browser.tabs.query({
+  let got = await browser.tabs.query({
     active: true, currentWindow: true
-  }).then((gotTabs) => {
-    if (gotTabs.length > 0) {
-      if (isNaN(keywordsStr)) {
-        return tabs.selectByKeyword(gotTabs[0], keywordsStr);
-      }
-      let index = parseInt(keywordsStr, 10) - 1;
-      return tabs.selectAt(index);
-    }
   });
+  if (got.length === 0) {
+    return;
+  }
+  if (isNaN(keywordsStr)) {
+    return tabs.selectByKeyword(got[0], keywordsStr);
+  }
+  let index = parseInt(keywordsStr, 10) - 1;
+  return tabs.selectAt(index);
 };
 
-const addBookmarkCommand = (tab, args) => {
+const addbookmarkCommand = async(tab, args) => {
   if (!args[0]) {
-    return Promise.resolve();
+    return;
   }
-
-  return bookmarks.create(args.join(' '), tab.url);
+  let item = await bookmarks.create(args.join(' '), tab.url);
+  if (!item) {
+    return browser.tabs.sendMessage(tab.id, {
+      type: messages.CONSOLE_SHOW_ERROR,
+      text: 'Could not create a bookmark',
+    });
+  }
+  return browser.tabs.sendMessage(tab.id, {
+    type: messages.CONSOLE_SHOW_INFO,
+    text: 'Saved current page: ' + item.url,
+  });
 };
 
 const setCommand = (args) => {
@@ -100,18 +107,7 @@ const exec = (tab, line, settings) => {
   case 'bdeletes!':
     return tabs.closeTabsByKeywordsForce(args.join(' '));
   case 'addbookmark':
-    return addBookmarkCommand(tab, args).then((item) => {
-      if (!item) {
-        return browser.tabs.sendMessage(tab.id, {
-          type: messages.CONSOLE_SHOW_ERROR,
-          text: 'Could not create a bookmark',
-        });
-      }
-      return browser.tabs.sendMessage(tab.id, {
-        type: messages.CONSOLE_SHOW_INFO,
-        text: 'Saved current page: ' + item.url,
-      });
-    });
+    return addbookmarkCommand(tab, args);
   case 'set':
     return setCommand(args);
   case 'q':
diff --git a/src/background/actions/setting.js b/src/background/actions/setting.js
index 773142f..7eeb5de 100644
--- a/src/background/actions/setting.js
+++ b/src/background/actions/setting.js
@@ -1,13 +1,12 @@
 import actions from '../actions';
 import * as settingsStorage from 'shared/settings/storage';
 
-const load = () => {
-  return settingsStorage.loadValue().then((value) => {
-    return {
-      type: actions.SETTING_SET_SETTINGS,
-      value,
-    };
-  });
+const load = async() => {
+  let value = await settingsStorage.loadValue();
+  return {
+    type: actions.SETTING_SET_SETTINGS,
+    value,
+  };
 };
 
 const setProperty = (name, value) => {
diff --git a/src/background/actions/tab.js b/src/background/actions/tab.js
index 0d439fd..5cf1e8c 100644
--- a/src/background/actions/tab.js
+++ b/src/background/actions/tab.js
@@ -1,19 +1,20 @@
 import actions from './index';
 
-const openNewTab = (url, openerTabId, background = false, adjacent = false) => {
-  if (adjacent) {
-    return browser.tabs.query({
-      active: true, currentWindow: true
-    }).then((tabs) => {
-      return browser.tabs.create({
-        url,
-        openerTabId,
-        active: !background,
-        index: tabs[0].index + 1
-      });
-    });
+const openNewTab = async(
+  url, openerTabId, background = false, adjacent = false
+) => {
+  if (!adjacent) {
+    return browser.tabs.create({ url, active: !background });
   }
-  return browser.tabs.create({ url, active: !background });
+  let tabs = await browser.tabs.query({
+    active: true, currentWindow: true
+  });
+  return browser.tabs.create({
+    url,
+    openerTabId,
+    active: !background,
+    index: tabs[0].index + 1
+  });
 };
 
 const openToTab = (url, tab) => {
diff --git a/src/background/components/background.js b/src/background/components/background.js
index 29124a6..c7a79a1 100644
--- a/src/background/components/background.js
+++ b/src/background/components/background.js
@@ -56,13 +56,12 @@ export default class BackgroundComponent {
     }
   }
 
-  broadcastSettingsChanged() {
-    return browser.tabs.query({}).then((tabs) => {
-      for (let tab of tabs) {
-        browser.tabs.sendMessage(tab.id, {
-          type: messages.SETTINGS_CHANGED,
-        });
-      }
-    });
+  async broadcastSettingsChanged() {
+    let tabs = await browser.tabs.query({});
+    for (let tab of tabs) {
+      browser.tabs.sendMessage(tab.id, {
+        type: messages.SETTINGS_CHANGED,
+      });
+    }
   }
 }
diff --git a/src/background/components/indicator.js b/src/background/components/indicator.js
index cceb119..1ded329 100644
--- a/src/background/components/indicator.js
+++ b/src/background/components/indicator.js
@@ -8,19 +8,17 @@ export default class IndicatorComponent {
     messages.onMessage(this.onMessage.bind(this));
 
     browser.browserAction.onClicked.addListener(this.onClicked);
-    browser.tabs.onActivated.addListener((info) => {
-      return browser.tabs.query({ currentWindow: true }).then(() => {
-        return this.onTabActivated(info);
-      });
+    browser.tabs.onActivated.addListener(async(info) => {
+      await browser.tabs.query({ currentWindow: true });
+      return this.onTabActivated(info);
     });
   }
 
-  onTabActivated(info) {
-    return browser.tabs.sendMessage(info.tabId, {
+  async onTabActivated(info) {
+    let { enabled } = await browser.tabs.sendMessage(info.tabId, {
       type: messages.ADDON_ENABLED_QUERY,
-    }).then((resp) => {
-      return this.updateIndicator(resp.enabled);
     });
+    return this.updateIndicator(enabled);
   }
 
   onClicked(tab) {
diff --git a/src/background/components/tab.js b/src/background/components/tab.js
index b273546..6af3fd7 100644
--- a/src/background/components/tab.js
+++ b/src/background/components/tab.js
@@ -4,10 +4,9 @@ export default class TabComponent {
   constructor(store) {
     this.store = store;
 
-    browser.tabs.onActivated.addListener((info) => {
-      return browser.tabs.query({ currentWindow: true }).then(() => {
-        return this.onTabActivated(info);
-      });
+    browser.tabs.onActivated.addListener(async(info) => {
+      await browser.tabs.query({ currentWindow: true });
+      return this.onTabActivated(info);
     });
   }
 
diff --git a/src/background/index.js b/src/background/index.js
index 3f1013c..02de53f 100644
--- a/src/background/index.js
+++ b/src/background/index.js
@@ -18,6 +18,15 @@ const store = createStore(reducers, (e, sender) => {
   }
 });
 
+const checkAndNotifyUpdated = async() => {
+  let updated = await versions.checkUpdated();
+  if (!updated) {
+    return;
+  }
+  await versions.notify();
+  await versions.commit();
+};
+
 /* eslint-disable no-unused-vars */
 const backgroundComponent = new BackgroundComponent(store);
 const operationComponent = new OperationComponent(store);
@@ -27,11 +36,4 @@ const indicatorComponent = new IndicatorComponent(store);
 
 store.dispatch(settingActions.load());
 
-versions.checkUpdated().then((updated) => {
-  if (!updated) {
-    return;
-  }
-  return versions.notify();
-}).then(() => {
-  return versions.commit();
-});
+checkAndNotifyUpdated();
diff --git a/src/background/shared/completions/bookmarks.js b/src/background/shared/completions/bookmarks.js
index 1adb350..bd753af 100644
--- a/src/background/shared/completions/bookmarks.js
+++ b/src/background/shared/completions/bookmarks.js
@@ -1,15 +1,14 @@
-const getCompletions = (keywords) => {
-  return browser.bookmarks.search({ query: keywords }).then((items) => {
-    return items.filter((item) => {
-      let url = undefined;
-      try {
-        url = new URL(item.url);
-      } catch (e) {
-        return false;
-      }
-      return item.type === 'bookmark' && url.protocol !== 'place:';
-    }).slice(0, 10);
-  });
+const getCompletions = async(keywords) => {
+  let items = await browser.bookmarks.search({ query: keywords });
+  return items.filter((item) => {
+    let url = undefined;
+    try {
+      url = new URL(item.url);
+    } catch (e) {
+      return false;
+    }
+    return item.type === 'bookmark' && url.protocol !== 'place:';
+  }).slice(0, 10);
 };
 
 export { getCompletions };
diff --git a/src/background/shared/completions/histories.js b/src/background/shared/completions/histories.js
index a7d3d47..2d35401 100644
--- a/src/background/shared/completions/histories.js
+++ b/src/background/shared/completions/histories.js
@@ -61,23 +61,22 @@ const reduceByOrigin = (items, min) => {
   return filtered;
 };
 
-const getCompletions = (keyword) => {
-  return browser.history.search({
+const getCompletions = async(keyword) => {
+  let historyItems = await browser.history.search({
     text: keyword,
     startTime: 0,
-  }).then((historyItems) => {
-    return [historyItems.map(item => [item, new URL(item.url)])]
-      .map(filterEmptyTitle)
-      .map(filterHttp)
-      .map(filterClosedPath)
-      .map(items => reduceByPathname(items, 10))
-      .map(items => reduceByOrigin(items, 10))
-      .map(items => items
-        .sort((x, y) => x[0].visitCount < y[0].visitCount)
-        .slice(0, 10)
-        .map(item => item[0])
-      )[0];
   });
+  return [historyItems.map(item => [item, new URL(item.url)])]
+    .map(filterEmptyTitle)
+    .map(filterHttp)
+    .map(filterClosedPath)
+    .map(items => reduceByPathname(items, 10))
+    .map(items => reduceByOrigin(items, 10))
+    .map(items => items
+      .sort((x, y) => x[0].visitCount < y[0].visitCount)
+      .slice(0, 10)
+      .map(item => item[0])
+    )[0];
 };
 
 export { getCompletions };
diff --git a/src/background/shared/completions/index.js b/src/background/shared/completions/index.js
index 728cee7..d5875fe 100644
--- a/src/background/shared/completions/index.js
+++ b/src/background/shared/completions/index.js
@@ -12,76 +12,66 @@ const getSearchCompletions = (command, keywords, searchConfig) => {
   return Promise.resolve(engineItems);
 };
 
-const getHistoryCompletions = (command, keywords) => {
-  return histories.getCompletions(keywords).then((pages) => {
-    return pages.map((page) => {
-      return {
-        caption: page.title,
-        content: command + ' ' + page.url,
-        url: page.url
-      };
-    });
+const getHistoryCompletions = async(command, keywords) => {
+  let items = await histories.getCompletions(keywords);
+  return items.map((page) => {
+    return {
+      caption: page.title,
+      content: command + ' ' + page.url,
+      url: page.url
+    };
   });
 };
 
-const getBookmarksCompletions = (command, keywords) => {
-  return bookmarks.getCompletions(keywords).then((items) => {
-    return items.map((item) => {
-      return {
-        caption: item.title,
-        content: command + ' ' + item.url,
-        url: item.url,
-      };
-    });
-  });
+const getBookmarksCompletions = async(command, keywords) => {
+  let items = await bookmarks.getCompletions(keywords);
+  return items.map(item => ({
+    caption: item.title,
+    content: command + ' ' + item.url,
+    url: item.url,
+  }));
 };
 
-const getOpenCompletions = (command, keywords, searchConfig) => {
-  return Promise.all([
-    getSearchCompletions(command, keywords, searchConfig),
-    getHistoryCompletions(command, keywords),
-    getBookmarksCompletions(command, keywords),
-  ]).then(([engineItems, historyItems, bookmarkItems]) => {
-    let completions = [];
-    if (engineItems.length > 0) {
-      completions.push({
-        name: 'Search Engines',
-        items: engineItems
-      });
-    }
-    if (historyItems.length > 0) {
-      completions.push({
-        name: 'History',
-        items: historyItems
-      });
-    }
-    if (bookmarkItems.length > 0) {
-      completions.push({
-        name: 'Bookmarks',
-        items: bookmarkItems
-      });
-    }
-    return completions;
-  });
+const getOpenCompletions = async(command, keywords, searchConfig) => {
+  let engineItems = await getSearchCompletions(command, keywords, searchConfig);
+  let historyItems = await getHistoryCompletions(command, keywords);
+  let bookmarkItems = await getBookmarksCompletions(command, keywords);
+  let completions = [];
+  if (engineItems.length > 0) {
+    completions.push({
+      name: 'Search Engines',
+      items: engineItems
+    });
+  }
+  if (historyItems.length > 0) {
+    completions.push({
+      name: 'History',
+      items: historyItems
+    });
+  }
+  if (bookmarkItems.length > 0) {
+    completions.push({
+      name: 'Bookmarks',
+      items: bookmarkItems
+    });
+  }
+  return completions;
 };
 
-const getBufferCompletions = (command, keywords, excludePinned) => {
-  return tabs.getCompletions(keywords, excludePinned).then((got) => {
-    let items = got.map((tab) => {
-      return {
-        caption: tab.title,
-        content: command + ' ' + tab.title,
-        url: tab.url,
-        icon: tab.favIconUrl
-      };
-    });
-    return [
-      {
-        name: 'Buffers',
-        items: items
-      }
-    ];
-  });
+const getBufferCompletions = async(command, keywords, excludePinned) => {
+  let items = await tabs.getCompletions(keywords, excludePinned);
+  items = items.map(tab => ({
+    caption: tab.title,
+    content: command + ' ' + tab.title,
+    url: tab.url,
+    icon: tab.favIconUrl
+  }));
+  return [
+    {
+      name: 'Buffers',
+      items: items
+    }
+  ];
 };
 
 const getCompletions = (line, settings) => {
diff --git a/src/background/shared/tabs.js b/src/background/shared/tabs.js
index 5c67a9f..33a4fac 100644
--- a/src/background/shared/tabs.js
+++ b/src/background/shared/tabs.js
@@ -1,143 +1,127 @@
 import * as tabCompletions from './completions/tabs';
 
-const closeTab = (id) => {
-  return browser.tabs.get(id).then((tab) => {
-    if (!tab.pinned) {
-      return browser.tabs.remove(id);
-    }
-  });
+const closeTab = async(id) => {
+  let tab = await browser.tabs.get(id);
+  if (!tab.pinned) {
+    return browser.tabs.remove(id);
+  }
 };
 
 const closeTabForce = (id) => {
   return browser.tabs.remove(id);
 };
 
-const queryByKeyword = (keyword, excludePinned = false) => {
-  return browser.tabs.query({ currentWindow: true }).then((tabs) => {
-    return tabs.filter((t) => {
-      return t.url.toLowerCase().includes(keyword.toLowerCase()) ||
-        t.title && t.title.toLowerCase().includes(keyword.toLowerCase());
-    }).filter((t) => {
-      return !(excludePinned && t.pinned);
-    });
+const queryByKeyword = async(keyword, excludePinned = false) => {
+  let tabs = await browser.tabs.query({ currentWindow: true });
+  return tabs.filter((t) => {
+    return t.url.toLowerCase().includes(keyword.toLowerCase()) ||
+      t.title && t.title.toLowerCase().includes(keyword.toLowerCase());
+  }).filter((t) => {
+    return !(excludePinned && t.pinned);
   });
 };
 
-const closeTabByKeywords = (keyword) => {
-  return queryByKeyword(keyword, false).then((tabs) => {
-    if (tabs.length === 0) {
-      throw new Error('No matching buffer for ' + keyword);
-    } else if (tabs.length > 1) {
-      throw new Error('More than one match for ' + keyword);
-    }
-    browser.tabs.remove(tabs[0].id);
-  });
-};
-
-const closeTabByKeywordsForce = (keyword) => {
-  return queryByKeyword(keyword, true).then((tabs) => {
-    if (tabs.length === 0) {
-      throw new Error('No matching buffer for ' + keyword);
-    } else if (tabs.length > 1) {
-      throw new Error('More than one match for ' + keyword);
-    }
-    browser.tabs.remove(tabs[0].id);
-  });
+const closeTabByKeywords = async(keyword) => {
+  let tabs = await queryByKeyword(keyword, false);
+  if (tabs.length === 0) {
+    throw new Error('No matching buffer for ' + keyword);
+  } else if (tabs.length > 1) {
+    throw new Error('More than one match for ' + keyword);
+  }
+  return browser.tabs.remove(tabs[0].id);
 };
 
-const closeTabsByKeywords = (keyword) => {
-  tabCompletions.getCompletions(keyword).then((tabs) => {
-    let tabs2 = tabs.filter(tab => !tab.pinned);
-    browser.tabs.remove(tabs2.map(tab => tab.id));
-  });
+const closeTabByKeywordsForce = async(keyword) => {
+  let tabs = await queryByKeyword(keyword, true);
+  if (tabs.length === 0) {
+    throw new Error('No matching buffer for ' + keyword);
+  } else if (tabs.length > 1) {
+    throw new Error('More than one match for ' + keyword);
+  }
+  return browser.tabs.remove(tabs[0].id);
 };
 
-const closeTabsByKeywordsForce = (keyword) => {
-  tabCompletions.getCompletions(keyword).then((tabs) => {
-    browser.tabs.remove(tabs.map(tab => tab.id));
-  });
+const closeTabsByKeywords = async(keyword) => {
+  let tabs = await tabCompletions.getCompletions(keyword);
+  tabs = tabs.filter(tab => !tab.pinned);
+  return browser.tabs.remove(tabs.map(tab => tab.id));
 };
 
-const reopenTab = () => {
-  let window = null;
-  return browser.windows.getCurrent().then().then((w) => {
-    window = w;
-    return browser.sessions.getRecentlyClosed();
-  }).then((sessions) => {
-    let session = sessions.find((s) => {
-      return s.tab && s.tab.windowId === window.id;
-    });
-    if (!session) {
-      return;
-    }
-    if (session.tab) {
-      return browser.sessions.restore(session.tab.sessionId);
-    }
-    return browser.sessions.restore(session.window.sessionId);
-  });
+const closeTabsByKeywordsForce = async(keyword) => {
+  let tabs = await tabCompletions.getCompletions(keyword);
+  return browser.tabs.remove(tabs.map(tab => tab.id));
 };
 
-const selectAt = (index) => {
-  return browser.tabs.query({ currentWindow: true }).then((tabs) => {
-    if (tabs.length < 2) {
-      return;
-    }
-    if (index < 0 || tabs.length <= index) {
-      throw new RangeError(`tab ${index + 1} does not exist`);
-    }
-    let id = tabs[index].id;
-    return browser.tabs.update(id, { active: true });
+const reopenTab = async() => {
+  let window = await browser.windows.getCurrent();
+  let sessions = await browser.sessions.getRecentlyClosed();
+  let session = sessions.find((s) => {
+    return s.tab && s.tab.windowId === window.id;
   });
+  if (!session) {
+    return;
+  }
+  if (session.tab) {
+    return browser.sessions.restore(session.tab.sessionId);
+  }
+  return browser.sessions.restore(session.window.sessionId);
+};
+
+const selectAt = async(index) => {
+  let tabs = await browser.tabs.query({ currentWindow: true });
+  if (tabs.length < 2) {
+    return;
+  }
+  if (index < 0 || tabs.length <= index) {
+    throw new RangeError(`tab ${index + 1} does not exist`);
+  }
+  let id = tabs[index].id;
+  return browser.tabs.update(id, { active: true });
 };
 
-const selectByKeyword = (current, keyword) => {
-  return queryByKeyword(keyword).then((tabs) => {
-    if (tabs.length === 0) {
-      throw new RangeError('No matching buffer for ' + keyword);
+const selectByKeyword = async(current, keyword) => {
+  let tabs = await queryByKeyword(keyword);
+  if (tabs.length === 0) {
+    throw new RangeError('No matching buffer for ' + keyword);
+  }
+  for (let tab of tabs) {
+    if (tab.index > current.index) {
+      return browser.tabs.update(tab.id, { active: true });
     }
-    for (let tab of tabs) {
-      if (tab.index > current.index) {
-        return browser.tabs.update(tab.id, { active: true });
-      }
-    }
-    return browser.tabs.update(tabs[0].id, { active: true });
-  });
+  }
+  return browser.tabs.update(tabs[0].id, { active: true });
 };
 
-const selectPrevTab = (current, count) => {
-  return browser.tabs.query({ currentWindow: true }).then((tabs) => {
-    if (tabs.length < 2) {
-      return;
-    }
-    let select = (current - count + tabs.length) % tabs.length;
-    let id = tabs[select].id;
-    return browser.tabs.update(id, { active: true });
-  });
+const selectPrevTab = async(current, count) => {
+  let tabs = await browser.tabs.query({ currentWindow: true });
+  if (tabs.length < 2) {
+    return;
+  }
+  let select = (current - count + tabs.length) % tabs.length;
+  let id = tabs[select].id;
+  return browser.tabs.update(id, { active: true });
 };
 
-const selectNextTab = (current, count) => {
-  return browser.tabs.query({ currentWindow: true }).then((tabs) => {
-    if (tabs.length < 2) {
-      return;
-    }
-    let select = (current + count) % tabs.length;
-    let id = tabs[select].id;
-    return browser.tabs.update(id, { active: true });
-  });
+const selectNextTab = async(current, count) => {
+  let tabs = await browser.tabs.query({ currentWindow: true });
+  if (tabs.length < 2) {
+    return;
+  }
+  let select = (current + count) % tabs.length;
+  let id = tabs[select].id;
+  return browser.tabs.update(id, { active: true });
 };
 
-const selectFirstTab = () => {
-  return browser.tabs.query({ currentWindow: true }).then((tabs) => {
-    let id = tabs[0].id;
-    return browser.tabs.update(id, { active: true });
-  });
+const selectFirstTab = async() => {
+  let tabs = await browser.tabs.query({ currentWindow: true });
+  let id = tabs[0].id;
+  return browser.tabs.update(id, { active: true });
 };
 
-const selectLastTab = () => {
-  return browser.tabs.query({ currentWindow: true }).then((tabs) => {
-    let id = tabs[tabs.length - 1].id;
-    return browser.tabs.update(id, { active: true });
-  });
+const selectLastTab = async() => {
+  let tabs = await browser.tabs.query({ currentWindow: true });
+  let id = tabs[tabs.length - 1].id;
+  return browser.tabs.update(id, { active: true });
 };
 
 const selectTab = (id) => {
@@ -152,14 +136,11 @@ const reload = (current, cache) => {
 };
 
 const updateTabPinned = (current, pinned) => {
-  return browser.tabs.query({ currentWindow: true, active: true })
-    .then(() => {
-      return browser.tabs.update(current.id, { pinned: pinned });
-    });
+  return browser.tabs.update(current.id, { pinned });
 };
 
 const toggleTabPinned = (current) => {
-  updateTabPinned(current, !current.pinned);
+  return updateTabPinned(current, !current.pinned);
 };
 
 const duplicate = (id) => {
diff --git a/src/background/shared/zooms.js b/src/background/shared/zooms.js
index e3e2aa6..17b28fa 100644
--- a/src/background/shared/zooms.js
+++ b/src/background/shared/zooms.js
@@ -9,26 +9,20 @@ const ZOOM_SETTINGS = [
   1.10, 1.25, 1.50, 1.75, 2.00, 2.50, 3.00
 ];
 
-const zoomIn = (tabId = undefined) => {
-  return browser.tabs.getZoom(tabId).then((factor) => {
-    for (let f of ZOOM_SETTINGS) {
-      if (f > factor) {
-        browser.tabs.setZoom(tabId, f);
-        break;
-      }
-    }
-  });
+const zoomIn = async(tabId = undefined) => {
+  let current = await browser.tabs.getZoom(tabId);
+  let factor = ZOOM_SETTINGS.find(f => f > current);
+  if (factor) {
+    return browser.tabs.setZoom(tabId, factor);
+  }
 };
 
-const zoomOut = (tabId = undefined) => {
-  return browser.tabs.getZoom(tabId).then((factor) => {
-    for (let f of [].concat(ZOOM_SETTINGS).reverse()) {
-      if (f < factor) {
-        browser.tabs.setZoom(tabId, f);
-        break;
-      }
-    }
-  });
+const zoomOut = async(tabId = undefined) => {
+  let current = await browser.tabs.getZoom(tabId);
+  let factor = [].concat(ZOOM_SETTINGS).reverse().find(f => f < current);
+  if (factor) {
+    return browser.tabs.setZoom(tabId, factor);
+  }
 };
 
 const neutral = (tabId = undefined) => {