diff --git a/CHANGELOG.md b/CHANGELOG.md
index 039a0ec08..e44ac75b6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,6 +28,7 @@ You should also include the user name that made the change.
 - Client: Improve deck UI @syuilo
 - Client: Word mute also checks content warnings @Johann150
 - Client: メニューからページをリロードできるように @syuilo
+- Client: Improve emoji picker performance @syuilo
 - ユーザーにモデレーションメモを残せる機能 @syuilo
 - Make possible to delete an account by admin @syuilo
 - Improve player detection in URL preview @mei23
diff --git a/package.json b/package.json
index d86750411..ccdfa727f 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
 	"name": "misskey",
-	"version": "12.112.0-beta.18",
+	"version": "12.112.0-beta.20",
 	"codename": "indigo",
 	"repository": {
 		"type": "git",
diff --git a/packages/backend/src/server/web/boot.js b/packages/backend/src/server/web/boot.js
index e82de8e14..9fc536555 100644
--- a/packages/backend/src/server/web/boot.js
+++ b/packages/backend/src/server/web/boot.js
@@ -106,39 +106,15 @@
 	function renderError(code, details) {
 		let errorsElement = document.getElementById('errors');
 		if (!errorsElement) {
-			document.getElementsByTagName("head")[0].insertAdjacentHTML(
-				"beforeend",
-				`<link rel="stylesheet" href="../error.css" />`);
 			document.documentElement.innerHTML = `
-			<svg class="icon-warning" xmlns="http://www.w3.org/2000/svg" class="icon icon-tabler icon-tabler-alert-triangle" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" fill="none" stroke-linecap="round" stroke-linejoin="round">
-   			<path stroke="none" d="M0 0h24v24H0z" fill="none"></path>
-   			<path d="M12 9v2m0 4v.01"></path>
-   			<path d="M5 19h14a2 2 0 0 0 1.84 -2.75l-7.1 -12.25a2 2 0 0 0 -3.5 0l-7.1 12.25a2 2 0 0 0 1.75 2.75"></path>
-			</svg>
-			<h1>An error has occurred!</h1>
-			<button class="button-big" onclick="location.reload(true);">
-				<span class="button-label-big">Refresh</span>
-			</button>
-      <p class="dont-worry">Don't worry, it's (probably) not your fault.</p>
-			<p>If the problem persists after refreshing, please contact your instance's administrator.<br>You may also try the following options:</p>
-      <a href="/flush">
-      <button class="button-small">
-        <span class="button-label-small">Flush preferences and cache</span>
-      </button>
-      </a>
-			<br>
-      <a href="/cli">
-        <button class="button-small">
-          <span class="button-label-small">Start the simple client</span>
-        </button>
-      </a>
-			<br>
-      <a href="/bios">
-        <button class="button-small">
-          <span class="button-label-small">Attempt to repair in Repair Tool</span>
-        </button>
-      </a>
-			<br>
+			<h1>⚠ An error has occurred. ⚠</h1>
+			<p>If the problem persists, please contact the administrator. You may also try the following options:</p>
+			<ul>
+				<li>Start <a href="/cli">the simple client</a></li>
+				<li>Attempt to repair in <a href="/bios">BIOS</a></li>
+				<li><a href="/flush">Flush preferences and cache</a></li>
+			</ul>
+			<hr>
 			<div id="errors"></div>
 			`;
 
@@ -146,7 +122,8 @@
 		}
 
 		const detailsElement = document.createElement('details');
-		detailsElement.innerHTML = `<br><summary><code>ERROR CODE: ${code}</code></summary>${JSON.stringify(details)}`;
+		detailsElement.innerHTML = `<summary><code>ERROR CODE: ${code}</code></summary>${JSON.stringify(details)}`;
+
 		errorsElement.appendChild(detailsElement);
 	}
 
diff --git a/packages/backend/src/server/web/views/base.pug b/packages/backend/src/server/web/views/base.pug
index 32499aa45..5bb156f0f 100644
--- a/packages/backend/src/server/web/views/base.pug
+++ b/packages/backend/src/server/web/views/base.pug
@@ -53,7 +53,7 @@ html
 		block meta
 
 		block og
-			meta(property='og:title'       content= title || 'Misskey')
+			meta(property='og:title'       content= title || 'Misskey') 
 			meta(property='og:description' content= desc || '✨🌎✨ A interplanetary communication platform ✨🚀✨') 
 			meta(property='og:image'       content= img)
 
diff --git a/packages/client/src/components/code-core.vue b/packages/client/src/components/code-core.vue
index a816f3480..b07402882 100644
--- a/packages/client/src/components/code-core.vue
+++ b/packages/client/src/components/code-core.vue
@@ -6,7 +6,7 @@
 
 <script lang="ts" setup>
 import { computed } from 'vue';
-import { Prism } from 'prismjs';
+import Prism from 'prismjs';
 import 'prismjs/themes/prism-okaidia.css';
 
 const props = defineProps<{
diff --git a/packages/client/src/components/emoji-picker.vue b/packages/client/src/components/emoji-picker.vue
index 2f974cbda..4a46e0ecf 100644
--- a/packages/client/src/components/emoji-picker.vue
+++ b/packages/client/src/components/emoji-picker.vue
@@ -59,11 +59,11 @@
 				</div>
 			</section>
 		</div>
-		<div class="group">
+		<div v-once class="group">
 			<header class="_acrylic">{{ i18n.ts.customEmojis }}</header>
 			<XSection v-for="category in customEmojiCategories" :key="'custom:' + category" :initial-shown="false" :emojis="customEmojis.filter(e => e.category === category).map(e => ':' + e.name + ':')" @chosen="chosen">{{ category || i18n.ts.other }}</XSection>
 		</div>
-		<div class="group">
+		<div v-once class="group">
 			<header class="_acrylic">{{ i18n.ts.emoji }}</header>
 			<XSection v-for="category in categories" :key="category" :emojis="emojilist.filter(e => e.category === category).map(e => e.char)" @chosen="chosen">{{ category }}</XSection>
 		</div>
diff --git a/packages/client/src/components/ui/menu.vue b/packages/client/src/components/ui/menu.vue
index cb4ec7c34..1f3d50897 100644
--- a/packages/client/src/components/ui/menu.vue
+++ b/packages/client/src/components/ui/menu.vue
@@ -136,7 +136,7 @@ function focusDown() {
 	> .item {
 		display: block;
 		position: relative;
-		padding: 6px 18px;
+		padding: 6px 16px;
 		width: 100%;
 		box-sizing: border-box;
 		white-space: nowrap;
diff --git a/packages/client/src/components/user-select-dialog.vue b/packages/client/src/components/user-select-dialog.vue
index b34d21af0..972d35348 100644
--- a/packages/client/src/components/user-select-dialog.vue
+++ b/packages/client/src/components/user-select-dialog.vue
@@ -11,7 +11,7 @@
 	<div class="tbhwbxda">
 		<div class="form">
 			<FormSplit :min-width="170">
-				<MkInput ref="usernameEl" v-model="username" @update:modelValue="search">
+				<MkInput v-model="username" :autofocus="true" @update:modelValue="search">
 					<template #label>{{ $ts.username }}</template>
 					<template #prefix>@</template>
 				</MkInput>
@@ -70,15 +70,8 @@ let host = $ref('');
 let users: misskey.entities.UserDetailed[] = $ref([]);
 let recentUsers: misskey.entities.UserDetailed[] = $ref([]);
 let selected: misskey.entities.UserDetailed | null = $ref(null);
-let usernameEl: HTMLElement = $ref();
 let dialogEl = $ref();
 
-const focus = () => {
-	if (usernameEl) {
-		usernameEl.focus();
-	}
-};
-
 const search = () => {
 	if (username === '' && host === '') {
 		users = [];
@@ -112,12 +105,6 @@ const cancel = () => {
 };
 
 onMounted(() => {
-	focus();
-
-	nextTick(() => {
-		focus();
-	});
-
 	os.api('users/show', {
 		userIds: defaultStore.state.recentlyUsedUsers,
 	}).then(users => {
diff --git a/packages/client/src/pages/settings/theme.vue b/packages/client/src/pages/settings/theme.vue
index 1bdad3e75..d330e1ba2 100644
--- a/packages/client/src/pages/settings/theme.vue
+++ b/packages/client/src/pages/settings/theme.vue
@@ -97,7 +97,10 @@ const darkThemeId = computed({
 		return darkTheme.value.id;
 	},
 	set(id) {
-		ColdDeviceStorage.set('darkTheme', themes.value.find(x => x.id === id));
+		const t = themes.value.find(x => x.id === id);
+		if (t) { // テーマエディタでテーマを作成したときなどは、themesに反映されないため undefined になる
+			ColdDeviceStorage.set('darkTheme', t);
+		}
 	},
 });
 const lightTheme = ColdDeviceStorage.ref('lightTheme');
@@ -106,7 +109,10 @@ const lightThemeId = computed({
 		return lightTheme.value.id;
 	},
 	set(id) {
-		ColdDeviceStorage.set('lightTheme', themes.value.find(x => x.id === id));
+		const t = themes.value.find(x => x.id === id);
+		if (t) { // テーマエディタでテーマを作成したときなどは、themesに反映されないため undefined になる
+			ColdDeviceStorage.set('lightTheme', t);
+		}
 	},
 });
 const darkMode = computed(defaultStore.makeGetterSetter('darkMode'));
diff --git a/packages/client/src/pages/theme-editor.vue b/packages/client/src/pages/theme-editor.vue
index 44b5a05f2..548e60614 100644
--- a/packages/client/src/pages/theme-editor.vue
+++ b/packages/client/src/pages/theme-editor.vue
@@ -192,7 +192,7 @@ async function saveAs() {
 	theme.name = name;
 	theme.author = `@${$i.username}@${toUnicode(host)}`;
 	if (description) theme.desc = description;
-	addTheme(theme);
+	await addTheme(theme);
 	applyTheme(theme);
 	if (defaultStore.state.darkMode) {
 		ColdDeviceStorage.set('darkTheme', theme);
diff --git a/packages/client/src/scripts/scroll.ts b/packages/client/src/scripts/scroll.ts
index 0643bad2f..f5bc6bf9c 100644
--- a/packages/client/src/scripts/scroll.ts
+++ b/packages/client/src/scripts/scroll.ts
@@ -2,12 +2,8 @@ type ScrollBehavior = 'auto' | 'smooth' | 'instant';
 
 export function getScrollContainer(el: HTMLElement | null): HTMLElement | null {
 	if (el == null || el.tagName === 'HTML') return null;
-	const overflow = window.getComputedStyle(el).getPropertyValue('overflow');
-	if (
-		// xとyを個別に指定している場合、`hidden scroll`みたいな値になる
-		overflow.endsWith('scroll') ||
-		overflow.endsWith('auto')
-	) {
+	const overflow = window.getComputedStyle(el).getPropertyValue('overflow-y');
+	if (overflow === 'scroll' || overflow === 'auto') {
 		return el;
 	} else {
 		return getScrollContainer(el.parentElement);
diff --git a/packages/client/src/store.ts b/packages/client/src/store.ts
index d87e05a4d..503333331 100644
--- a/packages/client/src/store.ts
+++ b/packages/client/src/store.ts
@@ -304,6 +304,14 @@ export class ColdDeviceStorage {
 	}
 
 	public static set<T extends keyof typeof ColdDeviceStorage.default>(key: T, value: typeof ColdDeviceStorage.default[T]): void {
+		// 呼び出し側のバグ等で undefined が来ることがある
+		// undefined を文字列として localStorage に入れると参照する際の JSON.parse でコケて不具合の元になるため無視
+		// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+		if (value === undefined) {
+			console.error(`attempt to store undefined value for key '${key}'`);
+			return;
+		}
+
 		localStorage.setItem(PREFIX + key, JSON.stringify(value));
 
 		for (const watcher of this.watchers) {