diff --git a/package.json b/package.json
index bd02cf06847e94372ac0e544049bd5df4a01d59b..eeabbe19feb400c151450533a50b8e8ddaa34392 100644
--- a/package.json
+++ b/package.json
@@ -23,7 +23,7 @@
     "react-dom": "^15"
   },
   "devDependencies": {
-    "autoprefixer": "6.7.7",
+    "autoprefixer": "7.1.0",
     "babel-core": "^6.23.1",
     "babel-eslint": "^7.1.1",
     "babel-loader": "^7.0.0",
@@ -32,11 +32,11 @@
     "babel-preset-react": "^6.22.0",
     "classnames": "2.2.5",
     "copy-webpack-plugin": "4.0.1",
-    "css-loader": "0.28.0",
+    "css-loader": "0.28.1",
     "eslint": "^3.16.1",
     "eslint-config-scratch": "^3.0.0",
-    "eslint-plugin-react": "^6.10.0",
-    "gh-pages": "^0.12.0",
+    "eslint-plugin-react": "^7.0.1",
+    "gh-pages": "^1.0.0",
     "html-webpack-plugin": "2.28.0",
     "lodash.bindall": "4.4.0",
     "lodash.debounce": "4.0.8",
@@ -46,17 +46,17 @@
     "lodash.pick": "4.4.0",
     "minilog": "3.1.0",
     "mkdirp": "^0.5.1",
-    "postcss-import": "9.1.0",
-    "postcss-loader": "1.3.3",
-    "postcss-simple-vars": "3.1.0",
-    "prop-types": "15.5.8",
+    "postcss-import": "^10.0.0",
+    "postcss-loader": "^2.0.5",
+    "postcss-simple-vars": "^4.0.0",
+    "prop-types": "^15.5.10",
     "react": "15.5.4",
     "react-dom": "15.5.4",
     "react-draggable": "2.2.6",
     "react-modal": "1.7.7",
-    "react-redux": "5.0.4",
+    "react-redux": "5.0.5",
     "react-style-proptype": "3.0.0",
-    "react-tabs": "0.8.3",
+    "react-tabs": "1.0.0",
     "redux": "3.6.0",
     "redux-throttle": "0.1.1",
     "rimraf": "^2.6.1",
@@ -65,7 +65,7 @@
     "scratch-render": "^0.1.0-prerelease.0",
     "scratch-storage": "^0.1.0",
     "scratch-vm": "^0.1.0-prerelease.0",
-    "style-loader": "0.16.1",
+    "style-loader": "^0.17.0",
     "svg-to-image": "1.1.3",
     "svg-url-loader": "2.0.2",
     "travis-after-all": "^1.4.4",
diff --git a/src/components/gui/gui.css b/src/components/gui/gui.css
index e2fe4db4333437657c6c3009fdde3c8df478b158..ebaf67d845cc1893abe6f63fc6fbfebcf04b19dd 100644
--- a/src/components/gui/gui.css
+++ b/src/components/gui/gui.css
@@ -47,7 +47,7 @@
     border-bottom: 0 !important;
 }
 
-.tab-list .tab {
+.tab {
     flex-grow: 1;
     height: 80%;
     margin-left: 1px;
@@ -63,9 +63,9 @@
     align-items: center;
 }
 
-
-.tab-list .tab[aria-selected="true"] {
+.tab.is-selected {
     color: #40B9F5;
+    background-color: #FFFFFF;
 }
 
 .tabs {
@@ -80,6 +80,10 @@
     position: relative;
     flex-grow: 1;
     flex-shrink: 0;
+    display: none;
+}
+
+.tab-panel.is-selected {
     display: flex;
 }
 
diff --git a/src/components/gui/gui.jsx b/src/components/gui/gui.jsx
index 9bf21c40de33d13d0edb32d36522bbcac7a728c0..47fb1b327a32a91fc25b4851a5e457b9364add5e 100644
--- a/src/components/gui/gui.jsx
+++ b/src/components/gui/gui.jsx
@@ -1,6 +1,10 @@
+const classNames = require('classnames');
 const PropTypes = require('prop-types');
 const React = require('react');
+const {Tab, Tabs, TabList, TabPanel} = require('react-tabs');
+const tabStyles = require('react-tabs/style/react-tabs.css');
 const VM = require('scratch-vm');
+
 const Blocks = require('../../containers/blocks.jsx');
 const CostumeTab = require('../../containers/costume-tab.jsx');
 const GreenFlag = require('../../containers/green-flag.jsx');
@@ -8,12 +12,13 @@ const TargetPane = require('../../containers/target-pane.jsx');
 const SoundTab = require('../../containers/sound-tab.jsx');
 const Stage = require('../../containers/stage.jsx');
 const StopAll = require('../../containers/stop-all.jsx');
-const MenuBar = require('../menu-bar/menu-bar.jsx');
-const {Tab, Tabs, TabList, TabPanel} = require('react-tabs');
 
 const Box = require('../box/box.jsx');
+const MenuBar = require('../menu-bar/menu-bar.jsx');
+
 const styles = require('./gui.css');
 
+
 const GUIComponent = props => {
     const {
         basePath,
@@ -31,6 +36,15 @@ const GUIComponent = props => {
         );
     }
 
+    const tabClassNames = {
+        tabs: styles.tabs,
+        tab: classNames(tabStyles.reactTabsTab, styles.tab),
+        tabList: classNames(tabStyles.reactTabsTabList, styles.tabList),
+        tabPanel: classNames(tabStyles.reactTabsTabPanel, styles.tabPanel),
+        tabPanelSelected: classNames(tabStyles.reactTabsTabPanelSelected, styles.isSelected),
+        tabSelected: classNames(tabStyles.reactTabsTabSelected, styles.isSelected)
+    };
+
     return (
         <Box
             className={styles.pageWrapper}
@@ -41,16 +55,18 @@ const GUIComponent = props => {
                 <Box className={styles.flexWrapper}>
                     <Box className={styles.editorWrapper}>
                         <Tabs
-                            className={styles.tabs}
+                            className={tabClassNames.tabs}
                             forceRenderTabPanel={true} // eslint-disable-line react/jsx-boolean-value
+                            selectedTabClassName={tabClassNames.tabSelected}
+                            selectedTabPanelClassName={tabClassNames.tabPanelSelected}
                             onSelect={onTabSelect}
                         >
-                            <TabList className={styles.tabList}>
-                                <Tab className={styles.tab}>Scripts</Tab>
-                                <Tab className={styles.tab}>Costumes</Tab>
-                                <Tab className={styles.tab}>Sounds</Tab>
+                            <TabList className={tabClassNames.tabList}>
+                                <Tab className={tabClassNames.tab}>Scripts</Tab>
+                                <Tab className={tabClassNames.tab}>Costumes</Tab>
+                                <Tab className={tabClassNames.tab}>Sounds</Tab>
                             </TabList>
-                            <TabPanel className={styles.tabPanel}>
+                            <TabPanel className={tabClassNames.tabPanel}>
                                 <Box className={styles.blocksWrapper}>
                                     <Blocks
                                         grow={1}
@@ -62,10 +78,10 @@ const GUIComponent = props => {
                                     />
                                 </Box>
                             </TabPanel>
-                            <TabPanel className={styles.tabPanel}>
+                            <TabPanel className={tabClassNames.tabPanel}>
                                 <CostumeTab vm={vm} />
                             </TabPanel>
-                            <TabPanel className={styles.tabPanel}>
+                            <TabPanel className={tabClassNames.tabPanel}>
                                 <SoundTab vm={vm} />
                             </TabPanel>
                         </Tabs>
diff --git a/src/components/library-item/library-item.css b/src/components/library-item/library-item.css
index e25c478d2af2147ee88ebccb472fa3d00fff69dc..c702492f8939412c2222f49bf0d99daa5076a33f 100644
--- a/src/components/library-item/library-item.css
+++ b/src/components/library-item/library-item.css
@@ -27,12 +27,6 @@
     transform: scale(1.02, 1.02);
 }
 
-.library-item.is-selected {
-    border-width: 2px;
-    border-color: #1dacf4;
-    transition: 0.25s ease-out;
-}
-
 .library-item-image-container {
     height: 100px;
 }
@@ -47,12 +41,12 @@
     margin: 0.25rem 0;
     text-align: center;
 
-    /* 
+    /*
         For truncating overflowing text gracefully
         Min-width is for a bug: https://css-tricks.com/flexbox-truncated-text
     */
     overflow: hidden;
     text-overflow: ellipsis;
     white-space: nowrap;
-    min-width: 0; 
+    min-width: 0;
 }
diff --git a/src/components/library-item/library-item.jsx b/src/components/library-item/library-item.jsx
index 31e722b0e8fd6cc9bb7d76cd24bd8fdf12cfe9e5..8e113c9be08af583a36272da486fe8afe31e0367 100644
--- a/src/components/library-item/library-item.jsx
+++ b/src/components/library-item/library-item.jsx
@@ -1,4 +1,3 @@
-const classNames = require('classnames');
 const bindAll = require('lodash.bindall');
 const PropTypes = require('prop-types');
 const React = require('react');
@@ -9,20 +8,29 @@ const styles = require('./library-item.css');
 class LibraryItem extends React.Component {
     constructor (props) {
         super(props);
-        bindAll(this, ['handleClick']);
+        bindAll(this, [
+            'handleClick',
+            'handleMouseEnter',
+            'handleMouseLeave'
+        ]);
     }
     handleClick (e) {
         this.props.onSelect(this.props.id);
         e.preventDefault();
     }
+    handleMouseEnter () {
+        this.props.onMouseEnter(this.props.id);
+    }
+    handleMouseLeave () {
+        this.props.onMouseLeave(this.props.id);
+    }
     render () {
         return (
             <Box
-                className={classNames({
-                    [styles.libraryItem]: true,
-                    [styles.isSelected]: this.props.selected
-                })}
+                className={styles.libraryItem}
                 onClick={this.handleClick}
+                onMouseEnter={this.handleMouseEnter}
+                onMouseLeave={this.handleMouseLeave}
             >
                 <Box className={styles.libraryItemImageContainer}>
                     <img
@@ -40,8 +48,9 @@ LibraryItem.propTypes = {
     iconURL: PropTypes.string.isRequired,
     id: PropTypes.number.isRequired,
     name: PropTypes.string.isRequired,
-    onSelect: PropTypes.func.isRequired,
-    selected: PropTypes.bool.isRequired
+    onMouseEnter: PropTypes.func.isRequired,
+    onMouseLeave: PropTypes.func.isRequired,
+    onSelect: PropTypes.func.isRequired
 };
 
 module.exports = LibraryItem;
diff --git a/src/components/library/library.jsx b/src/components/library/library.jsx
index 16327c10c80cb075658e28484465998bf1ce7c4c..71b29ff612ff1552eae7df150f2eaa9782a9120d 100644
--- a/src/components/library/library.jsx
+++ b/src/components/library/library.jsx
@@ -10,20 +10,21 @@ const styles = require('./library.css');
 class LibraryComponent extends React.Component {
     constructor (props) {
         super(props);
-        bindAll(this, ['handleSelect']);
-        this.state = {selectedItem: null};
+        bindAll(this, [
+            'handleSelect',
+            'handleMouseEnter',
+            'handleMouseLeave'
+        ]);
     }
     handleSelect (id) {
-        if (this.state.selectedItem === id) {
-            // Double select: select as the library's value.
-            this.props.onRequestClose();
-            this.props.onItemSelected(this.props.data[id]);
-        } else {
-            if (this.props.onItemChosen) {
-                this.props.onItemChosen(this.props.data[id]);
-            }
-        }
-        this.setState({selectedItem: id});
+        this.props.onRequestClose();
+        this.props.onItemSelected(this.props.data[id]);
+    }
+    handleMouseEnter (id) {
+        if (this.props.onItemMouseEnter) this.props.onItemMouseEnter(this.props.data[id]);
+    }
+    handleMouseLeave (id) {
+        if (this.props.onItemMouseLeave) this.props.onItemMouseLeave(this.props.data[id]);
     }
     render () {
         if (!this.props.visible) return null;
@@ -45,7 +46,8 @@ class LibraryComponent extends React.Component {
                                 id={itemId}
                                 key={`item_${itemId}`}
                                 name={dataItem.name}
-                                selected={this.state.selectedItem === itemId}
+                                onMouseEnter={this.handleMouseEnter}
+                                onMouseLeave={this.handleMouseLeave}
                                 onSelect={this.handleSelect}
                             />
                         );
@@ -67,7 +69,8 @@ LibraryComponent.propTypes = {
         })
         /* eslint-enable react/no-unused-prop-types, lines-around-comment */
     ),
-    onItemChosen: PropTypes.func,
+    onItemMouseEnter: PropTypes.func,
+    onItemMouseLeave: PropTypes.func,
     onItemSelected: PropTypes.func,
     onRequestClose: PropTypes.func,
     title: PropTypes.string.isRequired,
diff --git a/src/containers/backdrop-library.jsx b/src/containers/backdrop-library.jsx
index b19921b4c77605d0f1f8700d1e70e7e814aea283..62e9cd473a21a9db548868af3bd1d273bcc18359 100644
--- a/src/containers/backdrop-library.jsx
+++ b/src/containers/backdrop-library.jsx
@@ -4,7 +4,7 @@ const React = require('react');
 const VM = require('scratch-vm');
 
 const backdropLibraryContent = require('../lib/libraries/backdrops.json');
-const LibaryComponent = require('../components/library/library.jsx');
+const LibraryComponent = require('../components/library/library.jsx');
 
 
 class BackdropLibrary extends React.Component {
@@ -26,7 +26,7 @@ class BackdropLibrary extends React.Component {
     }
     render () {
         return (
-            <LibaryComponent
+            <LibraryComponent
                 data={backdropLibraryContent}
                 title="Backdrop Library"
                 visible={this.props.visible}
diff --git a/src/containers/costume-library.jsx b/src/containers/costume-library.jsx
index 1fea39a2dda106f7941084469c81fb0886f32130..d0a004ba674e37c4710c581ef1c72bd7658d798d 100644
--- a/src/containers/costume-library.jsx
+++ b/src/containers/costume-library.jsx
@@ -4,7 +4,7 @@ const React = require('react');
 const VM = require('scratch-vm');
 
 const costumeLibraryContent = require('../lib/libraries/costumes.json');
-const LibaryComponent = require('../components/library/library.jsx');
+const LibraryComponent = require('../components/library/library.jsx');
 
 
 class CostumeLibrary extends React.Component {
@@ -26,7 +26,7 @@ class CostumeLibrary extends React.Component {
     }
     render () {
         return (
-            <LibaryComponent
+            <LibraryComponent
                 data={costumeLibraryContent}
                 title="Costume Library"
                 visible={this.props.visible}
diff --git a/src/containers/costume-tab.jsx b/src/containers/costume-tab.jsx
index 24f54bc7832152757c7b0cfb9fcccc2050729d2c..af73857e75f5a2427da74c69e9f2ebc5b65769be 100644
--- a/src/containers/costume-tab.jsx
+++ b/src/containers/costume-tab.jsx
@@ -23,28 +23,25 @@ class CostumeTab extends React.Component {
         this.state = {selectedCostumeIndex: 0};
     }
 
+    componentWillReceiveProps (nextProps) {
+        const {
+            editingTarget,
+            sprites,
+            stage
+        } = nextProps;
+
+        const target = editingTarget && sprites[editingTarget] ? sprites[editingTarget] : stage;
+        if (target && target.costumes && this.state.selectedCostumeIndex > target.costumes.length - 1) {
+            this.setState({selectedCostumeIndex: target.costumes.length - 1});
+        }
+    }
+
     handleSelectCostume (costumeIndex) {
         this.setState({selectedCostumeIndex: costumeIndex});
     }
 
     handleDeleteCostume (costumeIndex) {
-        // @todo the VM should handle all of this logic
-        const {editingTarget} = this.props.vm;
-
-        if (costumeIndex === editingTarget.currentCostume) {
-            editingTarget.setCostume(costumeIndex - 1);
-        }
-
-        editingTarget.sprite.costumes = editingTarget.sprite.costumes
-            .slice(0, costumeIndex)
-            .concat(editingTarget.sprite.costumes.slice(costumeIndex + 1));
-        this.props.vm.runtime.requestTargetsUpdate(editingTarget);
-        // @todo not sure if this is getting redrawn correctly
-        this.props.vm.runtime.requestRedraw();
-
-        this.setState({
-            selectedCostumeIndex: this.state.selectedCostumeIndex % editingTarget.sprite.costumes.length
-        });
+        this.props.vm.deleteCostume(costumeIndex);
     }
 
     render () {
diff --git a/src/containers/sound-library.jsx b/src/containers/sound-library.jsx
index d478d141a7f6d8c538a03830b7583d4d39ad990c..53aa6bde02f9d54e0d394691549bd04416c7bce5 100644
--- a/src/containers/sound-library.jsx
+++ b/src/containers/sound-library.jsx
@@ -3,7 +3,7 @@ const PropTypes = require('prop-types');
 const React = require('react');
 const VM = require('scratch-vm');
 const AudioEngine = require('scratch-audio');
-const LibaryComponent = require('../components/library/library.jsx');
+const LibraryComponent = require('../components/library/library.jsx');
 
 const soundIcon = require('../components/asset-panel/icon--sound.svg');
 
@@ -14,14 +14,19 @@ class SoundLibrary extends React.Component {
         super(props);
         bindAll(this, [
             'handleItemSelected',
-            'handleItemChosen'
+            'handleItemMouseEnter',
+            'handleItemMouseLeave'
         ]);
     }
     componentDidMount () {
         this.audioEngine = new AudioEngine();
         this.player = this.audioEngine.createPlayer();
     }
-    handleItemChosen (soundItem) {
+    componentWillReceiveProps (newProps) {
+        // Stop playing sounds if the library closes without a mouseleave (e.g. by using the escape key)
+        if (this.player && !newProps.visible) this.player.stopAllSounds();
+    }
+    handleItemMouseEnter (soundItem) {
         const md5ext = soundItem._md5;
         const idParts = md5ext.split('.');
         const md5 = idParts[0];
@@ -39,6 +44,9 @@ class SoundLibrary extends React.Component {
             this.player.playSound(soundItem._md5);
         });
     }
+    handleItemMouseLeave () {
+        this.player.stopAllSounds();
+    }
     handleItemSelected (soundItem) {
         const vmSound = {
             format: soundItem.format,
@@ -64,11 +72,12 @@ class SoundLibrary extends React.Component {
         });
 
         return (
-            <LibaryComponent
+            <LibraryComponent
                 data={soundLibraryThumbnailData}
                 title="Sound Library"
                 visible={this.props.visible}
-                onItemChosen={this.handleItemChosen}
+                onItemMouseEnter={this.handleItemMouseEnter}
+                onItemMouseLeave={this.handleItemMouseLeave}
                 onItemSelected={this.handleItemSelected}
                 onRequestClose={this.props.onRequestClose}
             />
diff --git a/src/containers/sound-tab.jsx b/src/containers/sound-tab.jsx
index 227919dff524a8fee93616b2f1ba427feceef92a..70dfbdef7f6430f52dbb0d826e38cbfd58778fd8 100644
--- a/src/containers/sound-tab.jsx
+++ b/src/containers/sound-tab.jsx
@@ -23,6 +23,20 @@ class SoundTab extends React.Component {
         this.state = {selectedSoundIndex: 0};
     }
 
+    componentWillReceiveProps (nextProps) {
+        const {
+            editingTarget,
+            sprites,
+            stage
+        } = nextProps;
+
+        const target = editingTarget && sprites[editingTarget] ? sprites[editingTarget] : stage;
+
+        if (target && target.sounds && this.state.selectedSoundIndex > target.sounds.length - 1) {
+            this.setState({selectedSoundIndex: target.sounds.length - 1});
+        }
+    }
+
     handleSelectSound (soundIndex) {
         const sound = this.props.vm.editingTarget.sprite.sounds[soundIndex];
         this.props.vm.editingTarget.audioPlayer.playSound(sound.md5);
@@ -30,17 +44,7 @@ class SoundTab extends React.Component {
     }
 
     handleDeleteSound (soundIndex) {
-        // @todo the VM should handle all of this logic
-        const {editingTarget} = this.props.vm;
-        editingTarget.sprite.sounds = editingTarget.sprite.sounds
-            .slice(0, soundIndex)
-            .concat(editingTarget.sprite.sounds.slice(soundIndex + 1));
-        this.props.vm.emitTargetsUpdate();
-        this.props.vm.runtime.requestRedraw();
-
-        this.setState({
-            selectedSoundIndex: this.state.selectedSoundIndex % editingTarget.sprite.sounds.length
-        });
+        this.props.vm.deleteSound(soundIndex);
     }
 
     render () {
diff --git a/src/containers/sprite-library.jsx b/src/containers/sprite-library.jsx
index c08748eb2337728cd862fe051b78b0da03dfe22e..0a1bcaa3ebcad309733aa10c5f98faf25c68f56a 100644
--- a/src/containers/sprite-library.jsx
+++ b/src/containers/sprite-library.jsx
@@ -5,7 +5,7 @@ const VM = require('scratch-vm');
 
 const spriteLibraryContent = require('../lib/libraries/sprites.json');
 
-const LibaryComponent = require('../components/library/library.jsx');
+const LibraryComponent = require('../components/library/library.jsx');
 
 class SpriteLibrary extends React.Component {
     constructor (props) {
@@ -19,7 +19,7 @@ class SpriteLibrary extends React.Component {
     }
     render () {
         return (
-            <LibaryComponent
+            <LibraryComponent
                 data={spriteLibraryContent}
                 title="Sprite Library"
                 visible={this.props.visible}
diff --git a/src/lib/blocks.js b/src/lib/blocks.js
index cfd64d98f555686606109b458eefdaefa4ff692e..c0cf9e3ef107c1bbcbd22986d04ad9c6adfcd13d 100644
--- a/src/lib/blocks.js
+++ b/src/lib/blocks.js
@@ -9,7 +9,9 @@ module.exports = function (vm) {
                 {
                     type: 'field_dropdown',
                     name: name,
-                    options: start.concat(menuOptionsFn())
+                    options: function () {
+                        return start.concat(menuOptionsFn());
+                    }
                 }
             ],
             inputsInline: true,