diff --git a/meshchatx/src/frontend/components/DropDownMenu.vue b/meshchatx/src/frontend/components/DropDownMenu.vue
index 9671446..c930f62 100644
--- a/meshchatx/src/frontend/components/DropDownMenu.vue
+++ b/meshchatx/src/frontend/components/DropDownMenu.vue
@@ -21,11 +21,9 @@
             >
                 <div
                     v-if="isShowingMenu && dropdownPosition"
-                    class="overflow-hidden fixed z-[200] w-56 rounded-md bg-white dark:bg-zinc-800 shadow-lg border border-gray-200 dark:border-zinc-700 focus:outline-none"
-                    :style="{
-                        left: dropdownPosition.x + 'px',
-                        top: dropdownPosition.y + 'px',
-                    }"
+                    ref="dropdownPanel"
+                    class="overflow-x-hidden fixed z-[200] w-56 rounded-md bg-white dark:bg-zinc-800 shadow-lg border border-gray-200 dark:border-zinc-700 focus:outline-none"
+                    :style="dropdownPanelStyle"
                     @click.stop="hideMenu"
                 >
                     <slot name="items" />
@@ -36,6 +34,8 @@
 </template>
 
 <script>
+import { clampFloatingToViewport } from "../js/clampFloatingToViewport.js";
+
 export default {
     name: "DropDownMenu",
     data() {
@@ -44,6 +44,24 @@ export default {
             dropdownPosition: null,
         };
     },
+    computed: {
+        dropdownPanelStyle() {
+            if (!this.dropdownPosition) {
+                return {};
+            }
+            const style = {
+                left: `${this.dropdownPosition.x}px`,
+                top: `${this.dropdownPosition.y}px`,
+            };
+            if (this.dropdownPosition.maxHeight != null) {
+                style.maxHeight = `${this.dropdownPosition.maxHeight}px`;
+                style.overflowY = "auto";
+            } else {
+                style.overflow = "hidden";
+            }
+            return style;
+        },
+    },
     methods: {
         toggleMenu() {
             if (this.isShowingMenu) {
@@ -71,24 +89,22 @@ export default {
                 if (!button) return;
 
                 const buttonRect = button.getBoundingClientRect();
-                const estimatedHeight = 200;
-                const spaceBelow = window.innerHeight - buttonRect.bottom;
-                const spaceAbove = buttonRect.top;
+                const menuWidth = 224;
+                let x = buttonRect.right - menuWidth;
+                x = Math.min(Math.max(8, x), window.innerWidth - menuWidth - 8);
 
-                let x = buttonRect.right - 224;
-                if (x < 8) x = 8;
-                if (x + 224 > window.innerWidth) x = window.innerWidth - 224 - 8;
+                const spaceBelow = window.innerHeight - buttonRect.bottom - 4;
+                const spaceAbove = buttonRect.top - 8;
+                let y = spaceBelow >= spaceAbove ? buttonRect.bottom + 4 : Math.max(8, buttonRect.top - 200 - 4);
 
-                let y;
-                if (spaceBelow >= estimatedHeight || spaceBelow >= spaceAbove) {
-                    y = buttonRect.bottom + 4;
-                } else {
-                    y = buttonRect.top - estimatedHeight - 4;
-                }
-                if (y < 8) y = 8;
-                if (y + estimatedHeight > window.innerHeight - 8) y = window.innerHeight - estimatedHeight - 8;
-
-                this.dropdownPosition = { x, y };
+                this.dropdownPosition = { x, y, maxHeight: null };
+                this.$nextTick(() => {
+                    const panel = this.$refs.dropdownPanel;
+                    if (!panel) return;
+                    const rect = panel.getBoundingClientRect();
+                    const { left, top, maxHeight } = clampFloatingToViewport(rect.left, rect.top, rect.width, rect.height);
+                    this.dropdownPosition = { x: left, y: top, maxHeight };
+                });
             });
         },
     },
diff --git a/meshchatx/src/frontend/components/LanguageSelector.vue b/meshchatx/src/frontend/components/LanguageSelector.vue
index c15b9a8..a2e72ff 100644
--- a/meshchatx/src/frontend/components/LanguageSelector.vue
+++ b/meshchatx/src/frontend/components/LanguageSelector.vue
@@ -14,8 +14,9 @@
         <Teleport to="body">
             <div
                 v-if="isDropdownOpen"
+                ref="languageDropdown"
                 v-click-outside="closeDropdown"
-                class="fixed w-48 bg-white dark:bg-zinc-900 border border-gray-200 dark:border-zinc-800 rounded-2xl shadow-xl z-[9999] overflow-hidden"
+                class="fixed w-48 bg-white dark:bg-zinc-900 border border-gray-200 dark:border-zinc-800 rounded-2xl shadow-xl z-[9999] overflow-x-hidden"
                 :style="dropdownStyle"
             >
                 <div class="p-2">
@@ -42,6 +43,7 @@
 
 <script>
 import MaterialDesignIcon from "./MaterialDesignIcon.vue";
+import { clampFloatingToViewport } from "../js/clampFloatingToViewport.js";
 
 const localeModules = import.meta.glob("../locales/*.json", { eager: true });
 const discoveredLanguages = Object.entries(localeModules)
@@ -80,6 +82,7 @@ export default {
         return {
             isDropdownOpen: false,
             dropdownPosition: { top: 0, left: 0 },
+            dropdownMaxHeight: null,
         };
     },
     computed: {
@@ -90,10 +93,17 @@ export default {
             return discoveredLanguages;
         },
         dropdownStyle() {
-            return {
+            const style = {
                 top: `${this.dropdownPosition.top}px`,
                 left: `${this.dropdownPosition.left}px`,
             };
+            if (this.dropdownMaxHeight != null) {
+                style.maxHeight = `${this.dropdownMaxHeight}px`;
+                style.overflowY = "auto";
+            } else {
+                style.overflow = "hidden";
+            }
+            return style;
         },
     },
     methods: {
@@ -106,10 +116,19 @@ export default {
         updateDropdownPosition(event) {
             const button = event.currentTarget;
             const rect = button.getBoundingClientRect();
+            this.dropdownMaxHeight = null;
             this.dropdownPosition = {
                 top: rect.bottom + 8,
-                left: Math.max(8, rect.right - 192), // 192px is w-48
+                left: Math.max(8, rect.right - 192),
             };
+            this.$nextTick(() => {
+                const panel = this.$refs.languageDropdown;
+                if (!panel) return;
+                const pr = panel.getBoundingClientRect();
+                const { left, top, maxHeight } = clampFloatingToViewport(pr.left, pr.top, pr.width, pr.height);
+                this.dropdownPosition = { left, top };
+                this.dropdownMaxHeight = maxHeight;
+            });
         },
         closeDropdown() {
             this.isDropdownOpen = false;
diff --git a/meshchatx/src/frontend/components/NotificationBell.vue b/meshchatx/src/frontend/components/NotificationBell.vue
index c6fbacf..6ce111c 100644
--- a/meshchatx/src/frontend/components/NotificationBell.vue
+++ b/meshchatx/src/frontend/components/NotificationBell.vue
@@ -19,8 +19,9 @@
         <Teleport to="body">
             <div
                 v-if="isDropdownOpen"
+                ref="notificationDropdown"
                 v-click-outside="closeDropdown"
-                class="fixed w-80 sm:w-96 md:max-lg:w-80 lg:w-96 bg-white dark:bg-zinc-900 border border-gray-200 dark:border-zinc-800 rounded-2xl shadow-xl z-[9999] max-h-[500px] overflow-hidden flex flex-col"
+                class="fixed w-80 sm:w-96 md:max-lg:w-80 lg:w-96 bg-white dark:bg-zinc-900 border border-gray-200 dark:border-zinc-800 rounded-2xl shadow-xl z-[9999] max-h-[min(500px,calc(100vh-2rem))] overflow-hidden flex flex-col"
                 :style="dropdownStyle"
             >
                 <div class="p-4 border-b border-gray-200 dark:border-zinc-800">
@@ -147,6 +148,7 @@ import MaterialDesignIcon from "./MaterialDesignIcon.vue";
 import Utils from "../js/Utils";
 import WebSocketConnection from "../js/WebSocketConnection";
 import GlobalState from "../js/GlobalState";
+import { clampFloatingToViewport } from "../js/clampFloatingToViewport.js";
 
 export default {
     name: "NotificationBell",
@@ -177,15 +179,20 @@ export default {
             unreadCount: 0,
             reloadInterval: null,
             dropdownPosition: { top: 0, left: 0 },
+            dropdownMaxHeight: null,
             showHistory: false,
         };
     },
     computed: {
         dropdownStyle() {
-            return {
+            const style = {
                 top: `${this.dropdownPosition.top}px`,
                 left: `${this.dropdownPosition.left}px`,
             };
+            if (this.dropdownMaxHeight != null) {
+                style.maxHeight = `${this.dropdownMaxHeight}px`;
+            }
+            return style;
         },
     },
     beforeUnmount() {
@@ -224,18 +231,30 @@ export default {
                 if (hadNotifications) {
                     await this.loadNotifications({ updateList: false });
                 }
+                await this.$nextTick();
+                this.clampNotificationDropdown();
             }
         },
         updateDropdownPosition(event) {
             const button = event.currentTarget;
             const rect = button.getBoundingClientRect();
             const isMobile = window.innerWidth < 640;
-            const dropdownWidth = isMobile ? 320 : 384; // 80 (320px) or 96 (384px)
+            const dropdownWidth = isMobile ? 320 : 384;
 
+            this.dropdownMaxHeight = null;
             this.dropdownPosition = {
                 top: rect.bottom + 8,
                 left: Math.max(16, rect.right - dropdownWidth),
             };
+            this.$nextTick(() => this.clampNotificationDropdown());
+        },
+        clampNotificationDropdown() {
+            const panel = this.$refs.notificationDropdown;
+            if (!panel || !this.isDropdownOpen) return;
+            const pr = panel.getBoundingClientRect();
+            const { left, top, maxHeight } = clampFloatingToViewport(pr.left, pr.top, pr.width, pr.height);
+            this.dropdownPosition = { top, left };
+            this.dropdownMaxHeight = maxHeight;
         },
         closeDropdown() {
             this.isDropdownOpen = false;
@@ -251,6 +270,10 @@ export default {
                     await this.loadNotifications({ updateList: false });
                 }
             }
+            if (this.isDropdownOpen) {
+                await this.$nextTick();
+                this.clampNotificationDropdown();
+            }
         },
         async loadNotifications(options = {}) {
             const updateList = options.updateList !== false;
diff --git a/meshchatx/src/frontend/components/contextmenu/ContextMenuPanel.vue b/meshchatx/src/frontend/components/contextmenu/ContextMenuPanel.vue
index ada2d59..95655f8 100644
--- a/meshchatx/src/frontend/components/contextmenu/ContextMenuPanel.vue
+++ b/meshchatx/src/frontend/components/contextmenu/ContextMenuPanel.vue
@@ -3,9 +3,10 @@
 <template>
     <div
         v-if="show"
+        ref="panel"
         class="context-menu-panel"
         :class="panelClass"
-        :style="{ top: y + 'px', left: x + 'px' }"
+        :style="panelStyle"
         v-bind="$attrs"
     >
         <slot name="header" />
@@ -14,6 +15,8 @@
 </template>
 
 <script>
+import { clampFloatingToViewport } from "../../js/clampFloatingToViewport.js";
+
 export default {
     name: "ContextMenuPanel",
     inheritAttrs: false,
@@ -35,5 +38,90 @@ export default {
             default: "",
         },
     },
+    data() {
+        return {
+            adjustedLeft: 0,
+            adjustedTop: 0,
+            panelMaxHeight: null,
+            repositionRaf: null,
+        };
+    },
+    computed: {
+        panelStyle() {
+            const style = {
+                top: `${this.adjustedTop}px`,
+                left: `${this.adjustedLeft}px`,
+            };
+            if (this.panelMaxHeight != null) {
+                style.maxHeight = `${this.panelMaxHeight}px`;
+                style.overflowY = "auto";
+            }
+            return style;
+        },
+    },
+    watch: {
+        show: {
+            immediate: true,
+            handler(visible) {
+                this.cancelReposition();
+                if (!visible) {
+                    this.panelMaxHeight = null;
+                    return;
+                }
+                this.adjustedLeft = this.x;
+                this.adjustedTop = this.y;
+                this.panelMaxHeight = null;
+                this.scheduleReposition();
+            },
+        },
+        x() {
+            if (this.show) {
+                this.scheduleReposition();
+            }
+        },
+        y() {
+            if (this.show) {
+                this.scheduleReposition();
+            }
+        },
+    },
+    mounted() {
+        window.addEventListener("resize", this.onWindowResize);
+    },
+    beforeUnmount() {
+        window.removeEventListener("resize", this.onWindowResize);
+        this.cancelReposition();
+    },
+    methods: {
+        onWindowResize() {
+            if (this.show) {
+                this.repositionToViewport();
+            }
+        },
+        cancelReposition() {
+            if (this.repositionRaf != null) {
+                cancelAnimationFrame(this.repositionRaf);
+                this.repositionRaf = null;
+            }
+        },
+        scheduleReposition() {
+            this.cancelReposition();
+            this.repositionRaf = requestAnimationFrame(() => {
+                this.repositionRaf = null;
+                this.$nextTick(() => this.repositionToViewport());
+            });
+        },
+        repositionToViewport() {
+            const el = this.$refs.panel;
+            if (!el || !this.show) {
+                return;
+            }
+            const rect = el.getBoundingClientRect();
+            const { left, top, maxHeight } = clampFloatingToViewport(this.x, this.y, rect.width, rect.height);
+            this.adjustedLeft = left;
+            this.adjustedTop = top;
+            this.panelMaxHeight = maxHeight;
+        },
+    },
 };
 </script>
diff --git a/meshchatx/src/frontend/components/messages/ConversationViewer.vue b/meshchatx/src/frontend/components/messages/ConversationViewer.vue
index 8ef520a..77e80ff 100644
--- a/meshchatx/src/frontend/components/messages/ConversationViewer.vue
+++ b/meshchatx/src/frontend/components/messages/ConversationViewer.vue
@@ -1616,6 +1616,7 @@
 
 <script>
 import Utils from "../../js/Utils";
+import { clampFloatingToViewport } from "../../js/clampFloatingToViewport.js";
 import { isNearBottom, scrollContainerToBottom, shouldLoadPreviousMessages } from "./conversationScroll.js";
 import {
     isTelemetryOnly as isTelemetryOnlyMessage,
@@ -3332,10 +3333,13 @@ export default {
                 const mv = me.touches ? me.touches[0] : me;
                 const dx = mv.clientX - this.reactionDragState.startX;
                 const dy = mv.clientY - this.reactionDragState.startY;
-                this.reactionPickerPos = {
-                    x: this.reactionDragState.originX + dx,
-                    y: this.reactionDragState.originY + dy,
-                };
+                const panelEl = this.$refs.reactionPickerPanel;
+                if (!panelEl) return;
+                const pr = panelEl.getBoundingClientRect();
+                const nx = this.reactionDragState.originX + dx;
+                const ny = this.reactionDragState.originY + dy;
+                const { left, top } = clampFloatingToViewport(nx, ny, pr.width, pr.height);
+                this.reactionPickerPos = { x: left, y: top };
             };
             const onUp = () => {
                 document.removeEventListener("mousemove", onMove);
diff --git a/meshchatx/src/frontend/js/clampFloatingToViewport.js b/meshchatx/src/frontend/js/clampFloatingToViewport.js
new file mode 100644
index 0000000..44b9366
--- /dev/null
+++ b/meshchatx/src/frontend/js/clampFloatingToViewport.js
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: 0BSD
+
+/**
+ * Clamp top-left coordinates for a fixed-position panel so it stays on-screen.
+ *
+ * @param {number} preferredLeft
+ * @param {number} preferredTop
+ * @param {number} width
+ * @param {number} height
+ * @param {{ margin?: number }} [options]
+ * @returns {{ left: number, top: number, maxHeight: number | null }}
+ */
+export function clampFloatingToViewport(preferredLeft, preferredTop, width, height, options = {}) {
+    const margin = options.margin ?? 8;
+    const vw = window.innerWidth;
+    const vh = window.innerHeight;
+    const maxW = Math.max(0, vw - 2 * margin);
+    const maxH = Math.max(0, vh - 2 * margin);
+
+    let left = preferredLeft;
+    let top = preferredTop;
+
+    if (width <= maxW) {
+        left = Math.min(Math.max(margin, left), vw - width - margin);
+    } else {
+        left = margin;
+    }
+
+    let maxHeight = null;
+    if (height <= maxH) {
+        top = Math.min(Math.max(margin, top), vh - height - margin);
+    } else {
+        top = margin;
+        maxHeight = maxH;
+    }
+
+    return { left, top, maxHeight };
+}
diff --git a/tests/frontend/clampFloatingToViewport.test.js b/tests/frontend/clampFloatingToViewport.test.js
new file mode 100644
index 0000000..530c102
--- /dev/null
+++ b/tests/frontend/clampFloatingToViewport.test.js
@@ -0,0 +1,90 @@
+import { readFileSync } from "fs";
+import { join } from "path";
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import { clampFloatingToViewport } from "../../meshchatx/src/frontend/js/clampFloatingToViewport.js";
+
+function readSource(relativePath) {
+    return readFileSync(join(process.cwd(), relativePath), "utf8");
+}
+
+describe("clampFloatingToViewport", () => {
+    let innerWidth;
+    let innerHeight;
+
+    beforeEach(() => {
+        innerWidth = 800;
+        innerHeight = 600;
+        Object.defineProperty(window, "innerWidth", {
+            configurable: true,
+            get: () => innerWidth,
+        });
+        Object.defineProperty(window, "innerHeight", {
+            configurable: true,
+            get: () => innerHeight,
+        });
+    });
+
+    it("returns preferred position when panel fits inside the viewport", () => {
+        const { left, top, maxHeight } = clampFloatingToViewport(100, 120, 200, 150);
+        expect(left).toBe(100);
+        expect(top).toBe(120);
+        expect(maxHeight).toBeNull();
+    });
+
+    it("shifts left when the panel would extend past the right edge", () => {
+        const w = 200;
+        const { left, top, maxHeight } = clampFloatingToViewport(700, 50, w, 100);
+        expect(left).toBe(800 - w - 8);
+        expect(top).toBe(50);
+        expect(maxHeight).toBeNull();
+    });
+
+    it("shifts up when the panel would extend past the bottom edge", () => {
+        const h = 200;
+        const { left, top, maxHeight } = clampFloatingToViewport(40, 520, 160, h);
+        expect(left).toBe(40);
+        expect(top).toBe(600 - h - 8);
+        expect(maxHeight).toBeNull();
+    });
+
+    it("uses custom margin", () => {
+        const w = 100;
+        const { left } = clampFloatingToViewport(790, 10, w, 50, { margin: 16 });
+        expect(left).toBe(800 - w - 16);
+    });
+
+    it("returns maxHeight when content is taller than the viewport allows", () => {
+        innerHeight = 400;
+        Object.defineProperty(window, "innerHeight", {
+            configurable: true,
+            get: () => innerHeight,
+        });
+        const { left, top, maxHeight } = clampFloatingToViewport(10, 10, 200, 900);
+        expect(left).toBe(10);
+        expect(top).toBe(8);
+        expect(maxHeight).toBe(400 - 16);
+    });
+
+    it("pins wide panels to the left margin when wider than usable width", () => {
+        innerWidth = 300;
+        Object.defineProperty(window, "innerWidth", {
+            configurable: true,
+            get: () => innerWidth,
+        });
+        const { left } = clampFloatingToViewport(50, 10, 500, 40);
+        expect(left).toBe(8);
+    });
+});
+
+describe("clampFloatingToViewport wiring", () => {
+    it.each([
+        ["DropDownMenu.vue", "meshchatx/src/frontend/components/DropDownMenu.vue", 'ref="dropdownPanel"'],
+        ["LanguageSelector.vue", "meshchatx/src/frontend/components/LanguageSelector.vue", 'ref="languageDropdown"'],
+        ["NotificationBell.vue", "meshchatx/src/frontend/components/NotificationBell.vue", 'ref="notificationDropdown"'],
+        ["ConversationViewer.vue", "meshchatx/src/frontend/components/messages/ConversationViewer.vue", "onReactionPickerDragStart"],
+    ])("%s imports the helper and clamps floating UI", (_, relativePath, anchor) => {
+        const src = readSource(relativePath);
+        expect(src).toContain("clampFloatingToViewport");
+        expect(src).toContain(anchor);
+    });
+});
diff --git a/tests/frontend/contextMenuStyles.test.js b/tests/frontend/contextMenuStyles.test.js
index 1cf0c9d..7980959 100644
--- a/tests/frontend/contextMenuStyles.test.js
+++ b/tests/frontend/contextMenuStyles.test.js
@@ -27,6 +27,14 @@ describe("context menu styling", () => {
         expect(item).toContain("context-item");
     });
 
+    it("ContextMenuPanel clamps position to the viewport via clampFloatingToViewport", () => {
+        const panel = readProjectFile("meshchatx/src/frontend/components/contextmenu/ContextMenuPanel.vue");
+        expect(panel).toContain("clampFloatingToViewport");
+        expect(panel).toContain('ref="panel"');
+        expect(panel).toContain("repositionToViewport");
+        expect(panel).toContain("resize");
+    });
+
     it("uses ContextMenuPanel and ContextMenuItem on all right-click context menus", () => {
         const files = [
             "meshchatx/src/frontend/components/contacts/ContactsPage.vue",