diff --git a/.gitignore b/.gitignore
index 5f2d2f551..2bf38cad4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 npm-debug.log
 node_modules
+yarn.lock
 
 app/bower_components
 test/bower_components
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 25eb9b915..e7d4a09fe 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,13 +1,17 @@
 # Changelog
 
 ## Current Master
+
+- Add ability for internationalization.
+- Will now throw an error if the `to` field in txParams is not valid.
+- Will strip null values from the `to` field.
 - Fix flashing to Log in screen after logging in or restoring from seed phrase.
 - Increase tap areas for menu buttons on mobile
 - Change all fonts in new-ui onboarding to Roboto, size 400
 - Add a welcome screen to new-ui onboarding flow
 - Make new-ui create password screen responsive
 - Hide network dropdown before account is initialized
-- Add ability for internationalization.
+- Fix bug that could prevent MetaMask from saving the latest vault.
 
 ## 4.2.0 Tue Mar 06 2018
 
diff --git a/app/manifest.json b/app/manifest.json
index 6c5ed686b..6fcf6cd7c 100644
--- a/app/manifest.json
+++ b/app/manifest.json
@@ -56,6 +56,7 @@
   ],
   "permissions": [
     "storage",
+    "unlimitedStorage",
     "clipboardWrite",
     "http://localhost:8545/",
     "https://*.infura.io/"
diff --git a/app/scripts/background.js b/app/scripts/background.js
index 601ae0372..ef5513ec7 100644
--- a/app/scripts/background.js
+++ b/app/scripts/background.js
@@ -1,9 +1,11 @@
 const urlUtil = require('url')
 const endOfStream = require('end-of-stream')
 const pump = require('pump')
+const debounce = require('debounce-stream')
 const log = require('loglevel')
 const extension = require('extensionizer')
 const LocalStorageStore = require('obs-store/lib/localStorage')
+const LocalStore = require('./lib/local-store')
 const storeTransform = require('obs-store/lib/transform')
 const asStream = require('obs-store/lib/asStream')
 const ExtensionPlatform = require('./platforms/extension')
@@ -44,6 +46,8 @@ let openMetamaskTabsIDs = {}
 
 // state persistence
 const diskStore = new LocalStorageStore({ storageKey: STORAGE_KEY })
+const localStore = new LocalStore()
+let versionedData
 
 // initialization flow
 initialize().catch(log.error)
@@ -64,12 +68,23 @@ async function initialize () {
 async function loadStateFromPersistence () {
   // migrations
   const migrator = new Migrator({ migrations })
+
   // read from disk
-  let versionedData = diskStore.getState() || migrator.generateInitialState(firstTimeState)
+  // first from preferred, async API:
+  versionedData = (await localStore.get()) ||
+                  diskStore.getState() ||
+                  migrator.generateInitialState(firstTimeState)
+
   // migrate data
   versionedData = await migrator.migrateData(versionedData)
+  if (!versionedData) {
+    throw new Error('MetaMask - migrator returned undefined')
+  }
+
   // write to disk
+  if (localStore.isSupported) localStore.set(versionedData)
   diskStore.putState(versionedData)
+
   // return just the data
   return versionedData.data
 }
@@ -102,16 +117,30 @@ function setupController (initState) {
   // setup state persistence
   pump(
     asStream(controller.store),
+    debounce(1000),
     storeTransform(versionifyData),
-    asStream(diskStore)
+    storeTransform(syncDataWithExtension),
+    asStream(diskStore),
+    (error) => {
+      log.error('pump hit error', error)
+    }
   )
 
   function versionifyData (state) {
-    const versionedData = diskStore.getState()
     versionedData.data = state
     return versionedData
   }
 
+  function syncDataWithExtension(state) {
+    if (localStore.isSupported) {
+      localStore.set(state)
+      .catch((err) => {
+        log.error('error setting state in local store:', err)
+      })
+    }
+    return state
+  }
+
   //
   // connect to other contexts
   //
diff --git a/app/scripts/lib/local-store.js b/app/scripts/lib/local-store.js
new file mode 100644
index 000000000..1cf00dd30
--- /dev/null
+++ b/app/scripts/lib/local-store.js
@@ -0,0 +1,38 @@
+// We should not rely on local storage in an extension!
+// We should use this instead!
+// https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/storage/local
+
+const extension = require('extensionizer')
+const { promisify } = require('util')
+
+module.exports = class ExtensionStore {
+  constructor() {
+    this.isSupported = !!(extension.storage.local)
+    if (!this.isSupported) {
+      log.error('Storage local API not available.')
+    }
+    const local = extension.storage.local
+    this._get = promisify(local.get).bind(local)
+    this._set = promisify(local.set).bind(local)
+  }
+
+  async get() {
+    if (!this.isSupported) return undefined
+    const result = await this._get()
+    // extension.storage.local always returns an obj
+    // if the object is empty, treat it as undefined
+    if (isEmpty(result)) {
+      return undefined
+    } else {
+      return result
+    }
+  }
+
+  async set(state) {
+    return this._set(state)
+  }
+}
+
+function isEmpty(obj) {
+  return Object.keys(obj).length === 0
+}
diff --git a/app/scripts/lib/tx-gas-utils.js b/app/scripts/lib/tx-gas-utils.js
index 6f6ff7852..0fa9dd8d4 100644
--- a/app/scripts/lib/tx-gas-utils.js
+++ b/app/scripts/lib/tx-gas-utils.js
@@ -4,7 +4,7 @@ const {
   BnMultiplyByFraction,
   bnToHex,
 } = require('./util')
-const addHexPrefix = require('ethereumjs-util').addHexPrefix
+const { addHexPrefix, isValidAddress } = require('ethereumjs-util')
 const SIMPLE_GAS_COST = '0x5208' // Hex for 21000, cost of a simple send.
 
 /*
@@ -113,12 +113,14 @@ module.exports = class TxGasUtil {
     }
   }
   validateRecipient (txParams) {
-    if (txParams.to === '0x') {
+    if (txParams.to === '0x' || txParams.to === null ) {
       if (txParams.data) {
         delete txParams.to
       } else {
         throw new Error('Invalid recipient address')
       }
+    } else if ( txParams.to !== undefined && !isValidAddress(txParams.to) ) {
+      throw new Error('Invalid recipient address')
     }
     return txParams
   }
diff --git a/old-ui/app/keychains/hd/restore-vault.js b/old-ui/app/keychains/hd/restore-vault.js
index 222172dfd..d334d8e5f 100644
--- a/old-ui/app/keychains/hd/restore-vault.js
+++ b/old-ui/app/keychains/hd/restore-vault.js
@@ -140,6 +140,19 @@ RestoreVaultScreen.prototype.createNewVaultAndRestore = function () {
   // check seed
   var seedBox = document.querySelector('textarea.twelve-word-phrase')
   var seed = seedBox.value.trim()
+
+  // true if the string has more than a space between words.
+  if (seed.split('  ').length > 1) {
+    this.warning = 'there can only be a space between words'
+    this.props.dispatch(actions.displayWarning(this.warning))
+    return
+  }
+  // true if seed contains a character that is not between a-z or a space
+  if (!seed.match(/^[a-z ]+$/)) {
+    this.warning = 'seed words only have lowercase characters'
+    this.props.dispatch(actions.displayWarning(this.warning))
+    return
+  }
   if (seed.split(' ').length !== 12) {
     this.warning = 'seed phrases are 12 words long'
     this.props.dispatch(actions.displayWarning(this.warning))
diff --git a/package.json b/package.json
index a80b7e28e..00587ece6 100644
--- a/package.json
+++ b/package.json
@@ -72,6 +72,7 @@
     "clone": "^2.1.1",
     "copy-to-clipboard": "^3.0.8",
     "debounce": "^1.0.0",
+    "debounce-stream": "^2.0.0",
     "deep-extend": "^0.5.0",
     "detect-node": "^2.0.3",
     "disc": "^1.3.2",
diff --git a/ui/app/keychains/hd/restore-vault.js b/ui/app/keychains/hd/restore-vault.js
index d1761f17d..685094854 100644
--- a/ui/app/keychains/hd/restore-vault.js
+++ b/ui/app/keychains/hd/restore-vault.js
@@ -144,6 +144,19 @@ RestoreVaultScreen.prototype.createNewVaultAndRestore = function () {
   // check seed
   var seedBox = document.querySelector('textarea.twelve-word-phrase')
   var seed = seedBox.value.trim()
+
+  // true if the string has more than a space between words.
+  if (seed.split('  ').length > 1) {
+    this.warning = 'there can only a space between words'
+    this.props.dispatch(actions.displayWarning(this.warning))
+    return
+  }
+  // true if seed contains a character that is not between a-z or a space
+  if (!seed.match(/^[a-z ]+$/)) {
+    this.warning = 'seed words only have lowercase characters'
+    this.props.dispatch(actions.displayWarning(this.warning))
+    return
+  }
   if (seed.split(' ').length !== 12) {
     this.warning = 'seed phrases are 12 words long'
     this.props.dispatch(actions.displayWarning(this.warning))