diff --git a/js/src/modals/PasswordManager/store.js b/js/src/modals/PasswordManager/store.js
index c60576e0f..659543c28 100644
--- a/js/src/modals/PasswordManager/store.js
+++ b/js/src/modals/PasswordManager/store.js
@@ -133,7 +133,7 @@ export default class Store {
   }
 
   testPassword = (password) => {
-    this.setBusy(false);
+    this.setBusy(true);
 
     return this._api.parity
       .testPassword(this.address, password || this.validatePassword)
diff --git a/js/src/redux/providers/compilerActions.js b/js/src/redux/providers/compilerActions.js
deleted file mode 100644
index d638c03a2..000000000
--- a/js/src/redux/providers/compilerActions.js
+++ /dev/null
@@ -1,69 +0,0 @@
-// Copyright 2015, 2016 Parity Technologies (UK) Ltd.
-// This file is part of Parity.
-
-// Parity is free software: you can redistribute it and/or modify
-// it under the terms of the GNU General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-
-// Parity is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU General Public License for more details.
-
-// You should have received a copy of the GNU General Public License
-// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
-
-import PromiseWorker from 'promise-worker';
-import runtime from 'serviceworker-webpack-plugin/lib/runtime';
-
-let workerRegistration;
-
-// Setup the Service Worker
-if ('serviceWorker' in navigator) {
-  workerRegistration = runtime
-    .register()
-    .then(() => navigator.serviceWorker.ready)
-    .then((registration) => {
-      const _worker = registration.active;
-      _worker.controller = registration.active;
-      const worker = new PromiseWorker(_worker);
-
-      return worker;
-    });
-} else {
-  workerRegistration = Promise.reject('Service Worker is not available in your browser.');
-}
-
-export function setWorker (worker) {
-  return {
-    type: 'setWorker',
-    worker
-  };
-}
-
-export function setError (error) {
-  return {
-    type: 'setError',
-    error
-  };
-}
-
-export function setupWorker () {
-  return (dispatch, getState) => {
-    const state = getState();
-
-    if (state.compiler.worker) {
-      return;
-    }
-
-    workerRegistration
-      .then((worker) => {
-        dispatch(setWorker(worker));
-      })
-      .catch((error) => {
-        console.error('sw', error);
-        dispatch(setWorker(null));
-      });
-  };
-}
diff --git a/js/src/redux/providers/index.js b/js/src/redux/providers/index.js
index 6a000bdac..e1441c479 100644
--- a/js/src/redux/providers/index.js
+++ b/js/src/redux/providers/index.js
@@ -22,7 +22,7 @@ export Status from './status';
 export apiReducer from './apiReducer';
 export balancesReducer from './balancesReducer';
 export blockchainReducer from './blockchainReducer';
-export compilerReducer from './compilerReducer';
+export workerReducer from './workerReducer';
 export imagesReducer from './imagesReducer';
 export personalReducer from './personalReducer';
 export signerReducer from './signerReducer';
diff --git a/js/src/redux/providers/signerMiddleware.js b/js/src/redux/providers/signerMiddleware.js
index 018e01e59..ba51d3426 100644
--- a/js/src/redux/providers/signerMiddleware.js
+++ b/js/src/redux/providers/signerMiddleware.js
@@ -17,7 +17,7 @@
 import * as actions from './signerActions';
 
 import { inHex } from '~/api/format/input';
-import { Wallet } from '../../util/wallet';
+import { Signer } from '../../util/signer';
 
 export default class SignerMiddleware {
   constructor (api) {
@@ -58,6 +58,7 @@ export default class SignerMiddleware {
       promise
         .then((txHash) => {
           console.log('confirmRequest', id, txHash);
+
           if (!txHash) {
             store.dispatch(actions.errorConfirmRequest({ id, err: 'Unable to confirm.' }));
             return;
@@ -73,33 +74,49 @@ export default class SignerMiddleware {
 
     // Sign request in-browser
     const transaction = payload.sendTransaction || payload.signTransaction;
+
     if (wallet && transaction) {
-      (transaction.nonce.isZero()
+      const noncePromise = transaction.nonce.isZero()
         ? this._api.parity.nextNonce(transaction.from)
-        : Promise.resolve(transaction.nonce)
-      ).then(nonce => {
-        let txData = {
-          to: inHex(transaction.to),
-          nonce: inHex(transaction.nonce.isZero() ? nonce : transaction.nonce),
-          gasPrice: inHex(transaction.gasPrice),
-          gasLimit: inHex(transaction.gas),
-          value: inHex(transaction.value),
-          data: inHex(transaction.data)
-        };
+        : Promise.resolve(transaction.nonce);
 
-        try {
-          // NOTE: Derving the key takes significant amount of time,
-          // make sure to display some kind of "in-progress" state.
-          const signer = Wallet.fromJson(wallet, password);
-          const rawTx = signer.signTransaction(txData);
+      const { worker } = store.getState().worker;
 
-          handlePromise(this._api.signer.confirmRequestRaw(id, rawTx));
-        } catch (error) {
-          console.error(error);
+      const signerPromise = worker && worker._worker.state === 'activated'
+        ? worker
+          .postMessage({
+            action: 'getSignerSeed',
+            data: { wallet, password }
+          })
+          .then((result) => {
+            const seed = Buffer.from(result.data);
+            return new Signer(seed);
+          })
+        : Signer.fromJson(wallet, password);
+
+      // NOTE: Derving the key takes significant amount of time,
+      // make sure to display some kind of "in-progress" state.
+      return Promise
+        .all([ signerPromise, noncePromise ])
+        .then(([ signer, nonce ]) => {
+          const txData = {
+            to: inHex(transaction.to),
+            nonce: inHex(transaction.nonce.isZero() ? nonce : transaction.nonce),
+            gasPrice: inHex(transaction.gasPrice),
+            gasLimit: inHex(transaction.gas),
+            value: inHex(transaction.value),
+            data: inHex(transaction.data)
+          };
+
+          return signer.signTransaction(txData);
+        })
+        .then((rawTx) => {
+          return handlePromise(this._api.signer.confirmRequestRaw(id, rawTx));
+        })
+        .catch((error) => {
+          console.error(error.message);
           store.dispatch(actions.errorConfirmRequest({ id, err: error.message }));
-        }
-      });
-      return;
+        });
     }
 
     handlePromise(this._api.signer.confirmRequest(id, { gas, gasPrice }, password));
diff --git a/js/src/redux/providers/status.js b/js/src/redux/providers/status.js
index ef4c09224..6d0e24c6b 100644
--- a/js/src/redux/providers/status.js
+++ b/js/src/redux/providers/status.js
@@ -125,12 +125,13 @@ export default class Status {
           this._store.dispatch(statusCollection(status));
           this._status = status;
         }
+
+        nextTimeout();
       })
       .catch((error) => {
         console.error('_pollStatus', error);
+        nextTimeout();
       });
-
-    nextTimeout();
   }
 
   /**
diff --git a/js/src/redux/providers/worker.js b/js/src/redux/providers/worker.js
new file mode 100644
index 000000000..35ca0f173
--- /dev/null
+++ b/js/src/redux/providers/worker.js
@@ -0,0 +1,68 @@
+// Copyright 2015, 2016 Parity Technologies (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+import PromiseWorker from 'promise-worker';
+import runtime from 'serviceworker-webpack-plugin/lib/runtime';
+
+import { setWorker } from './workerActions';
+
+function getWorker () {
+  // Setup the Service Worker
+  if ('serviceWorker' in navigator) {
+    return runtime
+      .register()
+      .then(() => navigator.serviceWorker.ready)
+      .then((registration) => {
+        const worker = registration.active;
+        worker.controller = registration.active;
+
+        return new PromiseWorker(worker);
+      });
+  }
+
+  return Promise.reject('Service Worker is not available in your browser.');
+}
+
+export const setupWorker = (store) => {
+  const { dispatch, getState } = store;
+
+  const state = getState();
+  const stateWorker = state.worker.worker;
+
+  if (stateWorker !== undefined && !(stateWorker && stateWorker._worker.state === 'redundant')) {
+    return;
+  }
+
+  getWorker()
+    .then((worker) => {
+      if (worker) {
+        worker._worker.addEventListener('statechange', (event) => {
+          console.warn('worker state changed to', worker._worker.state);
+
+          // Re-install the new Worker
+          if (worker._worker.state === 'redundant') {
+            setupWorker(store);
+          }
+        });
+      }
+
+      dispatch(setWorker(worker));
+    })
+    .catch((error) => {
+      console.error('sw', error);
+      dispatch(setWorker(null));
+    });
+};
diff --git a/js/src/redux/providers/workerActions.js b/js/src/redux/providers/workerActions.js
new file mode 100644
index 000000000..50a877508
--- /dev/null
+++ b/js/src/redux/providers/workerActions.js
@@ -0,0 +1,29 @@
+// Copyright 2015, 2016 Parity Technologies (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+export function setWorker (worker) {
+  return {
+    type: 'setWorker',
+    worker
+  };
+}
+
+export function setError (error) {
+  return {
+    type: 'setError',
+    error
+  };
+}
diff --git a/js/src/redux/providers/compilerReducer.js b/js/src/redux/providers/workerReducer.js
similarity index 94%
rename from js/src/redux/providers/compilerReducer.js
rename to js/src/redux/providers/workerReducer.js
index e23bf3b16..27144e11b 100644
--- a/js/src/redux/providers/compilerReducer.js
+++ b/js/src/redux/providers/workerReducer.js
@@ -24,7 +24,7 @@ const initialState = {
 export default handleActions({
   setWorker (state, action) {
     const { worker } = action;
-    return Object.assign({}, state, { worker });
+    return Object.assign({}, state, { worker: worker || null });
   },
 
   setError (state, action) {
diff --git a/js/src/redux/reducers.js b/js/src/redux/reducers.js
index aac1ea779..1156d1836 100644
--- a/js/src/redux/reducers.js
+++ b/js/src/redux/reducers.js
@@ -19,7 +19,7 @@ import { routerReducer } from 'react-router-redux';
 
 import {
   apiReducer, balancesReducer, blockchainReducer,
-  compilerReducer, imagesReducer, personalReducer,
+  workerReducer, imagesReducer, personalReducer,
   signerReducer, statusReducer as nodeStatusReducer,
   snackbarReducer, walletReducer
 } from './providers';
@@ -40,12 +40,12 @@ export default function () {
     balances: balancesReducer,
     certifications: certificationsReducer,
     blockchain: blockchainReducer,
-    compiler: compilerReducer,
     images: imagesReducer,
     nodeStatus: nodeStatusReducer,
     personal: personalReducer,
     signer: signerReducer,
     snackbar: snackbarReducer,
-    wallet: walletReducer
+    wallet: walletReducer,
+    worker: workerReducer
   });
 }
diff --git a/js/src/redux/store.js b/js/src/redux/store.js
index dc043e242..9924aa461 100644
--- a/js/src/redux/store.js
+++ b/js/src/redux/store.js
@@ -20,6 +20,7 @@ import initMiddleware from './middleware';
 import initReducers from './reducers';
 
 import { load as loadWallet } from './providers/walletActions';
+import { setupWorker } from './providers/worker';
 
 import {
   Balances as BalancesProvider,
@@ -43,6 +44,7 @@ export default function (api, browserHistory) {
   new StatusProvider(store, api).start();
 
   store.dispatch(loadWallet(api));
+  setupWorker(store);
 
   return store;
 }
diff --git a/js/src/serviceWorker.js b/js/src/serviceWorker.js
index 136e6a6b7..3fdfc02ac 100644
--- a/js/src/serviceWorker.js
+++ b/js/src/serviceWorker.js
@@ -15,6 +15,7 @@
 // along with Parity.  If not, see <http://www.gnu.org/licenses/>.
 
 import registerPromiseWorker from 'promise-worker/register';
+import { Signer } from '~/util/signer';
 import SolidityUtils from '~/util/solidity';
 
 const CACHE_NAME = 'parity-cache-v1';
@@ -93,12 +94,21 @@ function handleMessage (message) {
     case 'setFiles':
       return setFiles(message.data);
 
+    case 'getSignerSeed':
+      return getSignerSeed(message.data);
+
     default:
       console.warn(`unknown action "${message.action}"`);
       return null;
   }
 }
 
+function getSignerSeed (data) {
+  console.log('deriving seed from service-worker');
+  const { wallet, password } = data;
+  return Signer.getSeed(wallet, password);
+}
+
 function compile (data) {
   const { build } = data;
 
diff --git a/js/src/ui/MethodDecoding/methodDecoding.css b/js/src/ui/MethodDecoding/methodDecoding.css
index adb899e1c..c782d6ce7 100644
--- a/js/src/ui/MethodDecoding/methodDecoding.css
+++ b/js/src/ui/MethodDecoding/methodDecoding.css
@@ -38,6 +38,10 @@
   justify-content: center;
 }
 
+.details {
+  line-height: 1.75em;
+}
+
 .details,
 .gasDetails {
   color: #aaa;
diff --git a/js/src/ui/MethodDecoding/methodDecoding.js b/js/src/ui/MethodDecoding/methodDecoding.js
index 59704a731..693ae60b5 100644
--- a/js/src/ui/MethodDecoding/methodDecoding.js
+++ b/js/src/ui/MethodDecoding/methodDecoding.js
@@ -196,7 +196,7 @@ class MethodDecoding extends Component {
       : text.slice(0, 50) + '...';
 
     return (
-      <div>
+      <div className={ styles.details }>
         <span>with the </span>
         <span
           onClick={ this.toggleInputType }
diff --git a/js/src/util/wallet.js b/js/src/util/signer.js
similarity index 83%
rename from js/src/util/wallet.js
rename to js/src/util/signer.js
index 81fe2859e..5d4442094 100644
--- a/js/src/util/wallet.js
+++ b/js/src/util/signer.js
@@ -24,9 +24,26 @@ import { sha3 } from '~/api/util/sha3';
 
 // Adapted from https://github.com/kvhnuke/etherwallet/blob/mercury/app/scripts/myetherwallet.js
 
-export class Wallet {
+export class Signer {
 
   static fromJson (json, password) {
+    return Signer
+      .getSeed(json, password)
+      .then((seed) => {
+        return new Signer(seed);
+      });
+  }
+
+  static getSeed (json, password) {
+    try {
+      const seed = Signer.getSyncSeed(json, password);
+      return Promise.resolve(seed);
+    } catch (error) {
+      return Promise.reject(error);
+    }
+  }
+
+  static getSyncSeed (json, password) {
     if (json.version !== 3) {
       throw new Error('Only V3 wallets are supported');
     }
@@ -43,15 +60,17 @@ export class Wallet {
       if (kdfparams.prf !== 'hmac-sha256') {
         throw new Error('Unsupported parameters to PBKDF2');
       }
+
       derivedKey = pbkdf2Sync(pwd, salt, kdfparams.c, kdfparams.dklen, 'sha256');
     } else {
       throw new Error('Unsupported key derivation scheme');
     }
 
     const ciphertext = Buffer.from(json.crypto.ciphertext, 'hex');
-    let mac = sha3(Buffer.concat([derivedKey.slice(16, 32), ciphertext]));
+    const mac = sha3(Buffer.concat([derivedKey.slice(16, 32), ciphertext]));
+
     if (mac !== inHex(json.crypto.mac)) {
-      throw new Error('Key derivation failed - possibly wrong passphrase');
+      throw new Error('Key derivation failed - possibly wrong password');
     }
 
     const decipher = createDecipheriv(
@@ -59,6 +78,7 @@ export class Wallet {
       derivedKey.slice(0, 16),
       Buffer.from(json.crypto.cipherparams.iv, 'hex')
     );
+
     let seed = Buffer.concat([decipher.update(ciphertext), decipher.final()]);
 
     while (seed.length < 32) {
@@ -66,7 +86,7 @@ export class Wallet {
       seed = Buffer.concat([nullBuff, seed]);
     }
 
-    return new Wallet(seed);
+    return seed;
   }
 
   constructor (seed) {
diff --git a/js/src/views/Signer/components/TransactionPendingForm/TransactionPendingFormConfirm/transactionPendingFormConfirm.js b/js/src/views/Signer/components/TransactionPendingForm/TransactionPendingFormConfirm/transactionPendingFormConfirm.js
index 99bd1c5f3..45eb3e5dd 100644
--- a/js/src/views/Signer/components/TransactionPendingForm/TransactionPendingFormConfirm/transactionPendingFormConfirm.js
+++ b/js/src/views/Signer/components/TransactionPendingForm/TransactionPendingFormConfirm/transactionPendingFormConfirm.js
@@ -77,13 +77,28 @@ class TransactionPendingFormConfirm extends Component {
     }
   }
 
+  getPasswordHint () {
+    const { account } = this.props;
+    const accountHint = account && account.meta && account.meta.passwordHint;
+
+    if (accountHint) {
+      return accountHint;
+    }
+
+    const { wallet } = this.state;
+    const walletHint = wallet && wallet.meta && wallet.meta.passwordHint;
+
+    return walletHint || null;
+  }
+
   render () {
     const { account, address, isSending } = this.props;
     const { password, wallet, walletError } = this.state;
     const isExternal = !account.uuid;
 
-    const passwordHint = account.meta && account.meta.passwordHint
-      ? (<div><span>(hint) </span>{ account.meta.passwordHint }</div>)
+    const passwordHintText = this.getPasswordHint();
+    const passwordHint = passwordHintText
+      ? (<div><span>(hint) </span>{ passwordHintText }</div>)
       : null;
 
     const isWalletOk = !isExternal || (walletError === null && wallet !== null);
@@ -170,12 +185,26 @@ class TransactionPendingFormConfirm extends Component {
   }
 
   onKeySelect = (event) => {
+    // Check that file have been selected
+    if (event.target.files.length === 0) {
+      return this.setState({
+        wallet: null,
+        walletError: null
+      });
+    }
+
     const fileReader = new FileReader();
 
     fileReader.onload = (e) => {
       try {
         const wallet = JSON.parse(e.target.result);
 
+        try {
+          if (wallet && typeof wallet.meta === 'string') {
+            wallet.meta = JSON.parse(wallet.meta);
+          }
+        } catch (e) {}
+
         this.setState({
           wallet,
           walletError: null
diff --git a/js/src/views/WriteContract/writeContract.js b/js/src/views/WriteContract/writeContract.js
index c013775a1..8a3ddf3d1 100644
--- a/js/src/views/WriteContract/writeContract.js
+++ b/js/src/views/WriteContract/writeContract.js
@@ -18,7 +18,6 @@ import React, { PropTypes, Component } from 'react';
 import { observer } from 'mobx-react';
 import { MenuItem, Toggle } from 'material-ui';
 import { connect } from 'react-redux';
-import { bindActionCreators } from 'redux';
 import CircularProgress from 'material-ui/CircularProgress';
 import moment from 'moment';
 import { throttle } from 'lodash';
@@ -32,8 +31,6 @@ import SendIcon from 'material-ui/svg-icons/content/send';
 import { Actionbar, ActionbarExport, ActionbarImport, Button, Editor, Page, Select, Input } from '~/ui';
 import { DeployContract, SaveContract, LoadContract } from '~/modals';
 
-import { setupWorker } from '~/redux/providers/compilerActions';
-
 import WriteContractStore from './writeContractStore';
 import styles from './writeContract.css';
 
@@ -42,7 +39,6 @@ class WriteContract extends Component {
 
   static propTypes = {
     accounts: PropTypes.object.isRequired,
-    setupWorker: PropTypes.func.isRequired,
     worker: PropTypes.object,
     workerError: PropTypes.any
   };
@@ -55,8 +51,7 @@ class WriteContract extends Component {
   };
 
   componentWillMount () {
-    const { setupWorker, worker } = this.props;
-    setupWorker();
+    const { worker } = this.props;
 
     if (worker !== undefined) {
       this.store.setWorker(worker);
@@ -575,17 +570,10 @@ class WriteContract extends Component {
 
 function mapStateToProps (state) {
   const { accounts } = state.personal;
-  const { worker, error } = state.compiler;
+  const { worker, error } = state.worker;
   return { accounts, worker, workerError: error };
 }
 
-function mapDispatchToProps (dispatch) {
-  return bindActionCreators({
-    setupWorker
-  }, dispatch);
-}
-
 export default connect(
-  mapStateToProps,
-  mapDispatchToProps
+  mapStateToProps
 )(WriteContract);