diff --git a/package-lock.json b/package-lock.json
index c4bcdac3e..f3aeef059 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "webbrain",
-  "version": "25.8.5",
+  "version": "25.8.6",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "webbrain",
-      "version": "25.8.5",
+      "version": "25.8.6",
       "license": "MIT",
       "devDependencies": {
         "playwright": "^1.48.0"
diff --git a/package.json b/package.json
index e2b5fc734..8152e02f8 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "webbrain",
-  "version": "25.8.5",
+  "version": "25.8.6",
   "description": "Open-source AI browser agent — chat with pages, automate tasks, multi-provider LLM support.",
   "private": true,
   "type": "module",
diff --git a/src/chrome/ARCHITECTURE.md b/src/chrome/ARCHITECTURE.md
index 993c27501..339d7d66d 100644
--- a/src/chrome/ARCHITECTURE.md
+++ b/src/chrome/ARCHITECTURE.md
@@ -1,6 +1,6 @@
 # WebBrain Chrome/Edge Extension — Architecture
 
-> Version 25.8.5 · Manifest V3 · Service Worker background
+> Version 25.8.6 · Manifest V3 · Service Worker background
 
 ## High-Level Overview
 
diff --git a/src/chrome/manifest.json b/src/chrome/manifest.json
index b9b7f9621..e0d5818b6 100644
--- a/src/chrome/manifest.json
+++ b/src/chrome/manifest.json
@@ -1,7 +1,7 @@
 {
   "manifest_version": 3,
   "name": "WebBrain",
-  "version": "25.8.5",
+  "version": "25.8.6",
   "description": "Open-source AI browser agent — chat with pages, automate tasks, multi-provider LLM support.",
   "permissions": [
     "sidePanel",
diff --git a/src/chrome/src/ui/settings.js b/src/chrome/src/ui/settings.js
index 33d3111d5..f788e950f 100644
--- a/src/chrome/src/ui/settings.js
+++ b/src/chrome/src/ui/settings.js
@@ -47,7 +47,7 @@ import { ADDITIONAL_PROVIDER_UI } from '../providers/provider-catalog.js';
 
 // Version shown in the subtitle. Kept here so it only needs one update per
 // release; the subtitle string itself is translated.
-const EXT_VERSION = '25.8.5';
+const EXT_VERSION = '25.8.6';
 
 const providersContainer = document.getElementById('providers');
 const displaySettings = document.getElementById('display-settings');
diff --git a/src/chrome/src/ui/sidepanel.js b/src/chrome/src/ui/sidepanel.js
index e846a8f50..780e34210 100644
--- a/src/chrome/src/ui/sidepanel.js
+++ b/src/chrome/src/ui/sidepanel.js
@@ -523,6 +523,14 @@ const activityText = document.getElementById('activity-text');
 const modeAskBtn = document.getElementById('btn-mode-ask');
 const modeActBtn = document.getElementById('btn-mode-act');
 const modeDevBtn = document.getElementById('btn-mode-dev');
+const modeToggleEl = document.getElementById('mode-toggle');
+const modeToggleHighlight = (() => {
+  const el = document.createElement('div');
+  el.className = 'mode-toggle-highlight instant';
+  el.setAttribute('aria-hidden', 'true');
+  modeToggleEl?.prepend(el);
+  return el;
+})();
 const actWarning = document.getElementById('act-warning');
 const inputArea = document.getElementById('input-area');
 const slashCommandMenuEl = document.getElementById('slash-command-menu');
@@ -9503,6 +9511,14 @@ async function handleGlobalKeydown(e) {
 
 // --- Mode Toggle ---
 
+function positionModeHighlight(btn, { instant = false } = {}) {
+  if (!modeToggleHighlight || !btn) return;
+  if (instant) modeToggleHighlight.classList.add('instant');
+  modeToggleHighlight.style.width = `${btn.offsetWidth}px`;
+  modeToggleHighlight.style.transform = `translate3d(${btn.offsetLeft}px, 0, 0)`;
+  if (instant) requestAnimationFrame(() => modeToggleHighlight.classList.remove('instant'));
+}
+
 function setMode(mode) {
   if (mode !== 'ask' && mode !== 'act' && mode !== 'dev') mode = 'ask';
   const previousMode = agentMode;
@@ -9521,6 +9537,12 @@ function setMode(mode) {
   modeDevBtn?.classList.toggle('active', mode === 'dev');
   modeDevBtn?.classList.toggle('act', mode === 'dev');
   inputArea.classList.toggle('act-mode', mode !== 'ask');
+
+  // Slide the highlight pill to the active button
+  const activeBtn = mode === 'ask' ? modeAskBtn : mode === 'act' ? modeActBtn : modeDevBtn;
+  modeToggleHighlight?.classList.toggle('act', mode !== 'ask');
+  positionModeHighlight(activeBtn);
+
   updateActWarning();
   resetInputPlaceholderRotation();
 }
@@ -9559,6 +9581,24 @@ modeDevBtn?.addEventListener('click', async () => {
   await ensureDevMode();
 });
 
+// Set initial highlight position without animation
+requestAnimationFrame(() => positionModeHighlight(modeAskBtn, { instant: true }));
+
+// Recalculate highlight when the toggle resizes (e.g. side panel drag)
+if (modeToggleEl) {
+  new ResizeObserver(() => {
+    const activeBtn = modeToggleEl.querySelector('.mode-btn.active');
+    if (activeBtn) positionModeHighlight(activeBtn, { instant: true });
+  }).observe(modeToggleEl);
+}
+
+// Reposition highlight when document direction changes (RTL locale switch)
+new MutationObserver(() => {
+  requestAnimationFrame(() => {
+    const activeBtn = modeToggleEl?.querySelector('.mode-btn.active');
+    if (activeBtn) positionModeHighlight(activeBtn, { instant: true });
+  });
+}).observe(document.documentElement, { attributes: true, attributeFilter: ['dir'] });
 
 // --- Stop / Abort ---
 
diff --git a/src/chrome/styles/sidepanel.css b/src/chrome/styles/sidepanel.css
index 9f0026b49..518e821a3 100644
--- a/src/chrome/styles/sidepanel.css
+++ b/src/chrome/styles/sidepanel.css
@@ -2112,10 +2112,37 @@ body {
   border: 1px solid var(--border);
   border-radius: 8px;
   padding: 2px;
+  position: relative;
+}
+
+.mode-toggle-highlight {
+  position: absolute;
+  top: 2px;
+  left: 0;
+  z-index: 0;
+  height: calc(100% - 4px);
+  border-radius: 6px;
+  background: var(--accent-dim);
+  pointer-events: none;
+  will-change: transform, width;
+  transition:
+    transform 170ms cubic-bezier(0.22, 1, 0.36, 1),
+    width 170ms cubic-bezier(0.22, 1, 0.36, 1),
+    background 170ms ease;
+}
+
+.mode-toggle-highlight.act {
+  background: rgba(255, 152, 0, 0.12);
+}
+
+.mode-toggle-highlight.instant {
+  transition: none;
 }
 
 .mode-btn {
   flex: 1;
+  position: relative;
+  z-index: 1;
   background: none;
   border: none;
   color: var(--text-muted);
@@ -2124,7 +2151,7 @@ body {
   padding: 5px 0;
   border-radius: 6px;
   cursor: pointer;
-  transition: all 0.2s;
+  transition: color 0.2s;
   text-align: center;
 }
 
@@ -2133,12 +2160,10 @@ body {
 }
 
 .mode-btn.active {
-  background: var(--accent-dim);
   color: var(--accent);
 }
 
 .mode-btn.active.act {
-  background: rgba(255, 152, 0, 0.12);
   color: var(--warning);
 }
 
diff --git a/src/firefox/ARCHITECTURE.md b/src/firefox/ARCHITECTURE.md
index df3cb1639..fb07f4d43 100644
--- a/src/firefox/ARCHITECTURE.md
+++ b/src/firefox/ARCHITECTURE.md
@@ -1,6 +1,6 @@
 # WebBrain Firefox Extension — Architecture
 
-> Version 25.8.5 · Manifest V2 · Background Page
+> Version 25.8.6 · Manifest V2 · Background Page
 
 ## How Firefox Differs from Chrome
 
diff --git a/src/firefox/manifest.json b/src/firefox/manifest.json
index c865be5b8..a0041e65a 100644
--- a/src/firefox/manifest.json
+++ b/src/firefox/manifest.json
@@ -1,7 +1,7 @@
 {
   "manifest_version": 2,
   "name": "WebBrain",
-  "version": "25.8.5",
+  "version": "25.8.6",
   "description": "Open-source AI browser agent — chat with pages, automate tasks, multi-provider LLM support.",
   "permissions": [
     "activeTab",
diff --git a/src/firefox/src/ui/settings.js b/src/firefox/src/ui/settings.js
index 87eedbab7..3aebfcdc3 100644
--- a/src/firefox/src/ui/settings.js
+++ b/src/firefox/src/ui/settings.js
@@ -47,7 +47,7 @@ import { ADDITIONAL_PROVIDER_UI } from '../providers/provider-catalog.js';
 
 // Version shown in the subtitle. Kept here so it only needs one update per
 // release; the subtitle string itself is translated.
-const EXT_VERSION = '25.8.5';
+const EXT_VERSION = '25.8.6';
 
 const providersContainer = document.getElementById('providers');
 const displaySettings = document.getElementById('display-settings');
diff --git a/src/firefox/src/ui/sidepanel.js b/src/firefox/src/ui/sidepanel.js
index 25c14a97e..3d3bf63a8 100644
--- a/src/firefox/src/ui/sidepanel.js
+++ b/src/firefox/src/ui/sidepanel.js
@@ -398,6 +398,14 @@ const activityText = document.getElementById('activity-text');
 const modeAskBtn = document.getElementById('btn-mode-ask');
 const modeActBtn = document.getElementById('btn-mode-act');
 const modeDevBtn = document.getElementById('btn-mode-dev');
+const modeToggleEl = document.getElementById('mode-toggle');
+const modeToggleHighlight = (() => {
+  const el = document.createElement('div');
+  el.className = 'mode-toggle-highlight instant';
+  el.setAttribute('aria-hidden', 'true');
+  modeToggleEl?.prepend(el);
+  return el;
+})();
 const actWarning = document.getElementById('act-warning');
 const inputArea = document.getElementById('input-area');
 const slashCommandMenuEl = document.getElementById('slash-command-menu');
@@ -9073,6 +9081,14 @@ async function sendToBackground(action, data = {}) {
 
 // --- Mode Toggle ---
 
+function positionModeHighlight(btn, { instant = false } = {}) {
+  if (!modeToggleHighlight || !btn) return;
+  if (instant) modeToggleHighlight.classList.add('instant');
+  modeToggleHighlight.style.width = `${btn.offsetWidth}px`;
+  modeToggleHighlight.style.transform = `translate3d(${btn.offsetLeft}px, 0, 0)`;
+  if (instant) requestAnimationFrame(() => modeToggleHighlight.classList.remove('instant'));
+}
+
 function setMode(mode) {
   if (mode !== 'ask' && mode !== 'act' && mode !== 'dev') mode = 'ask';
   agentMode = mode;
@@ -9084,6 +9100,12 @@ function setMode(mode) {
   modeDevBtn?.classList.toggle('active', mode === 'dev');
   modeDevBtn?.classList.toggle('act', mode === 'dev');
   inputArea.classList.toggle('act-mode', mode !== 'ask');
+
+  // Slide the highlight pill to the active button
+  const activeBtn = mode === 'ask' ? modeAskBtn : mode === 'act' ? modeActBtn : modeDevBtn;
+  modeToggleHighlight?.classList.toggle('act', mode !== 'ask');
+  positionModeHighlight(activeBtn);
+
   updateActWarning();
   resetInputPlaceholderRotation();
 }
@@ -9122,6 +9144,24 @@ modeDevBtn?.addEventListener('click', async () => {
   await ensureDevMode();
 });
 
+// Set initial highlight position without animation
+requestAnimationFrame(() => positionModeHighlight(modeAskBtn, { instant: true }));
+
+// Recalculate highlight when the toggle resizes (e.g. side panel drag)
+if (modeToggleEl) {
+  new ResizeObserver(() => {
+    const activeBtn = modeToggleEl.querySelector('.mode-btn.active');
+    if (activeBtn) positionModeHighlight(activeBtn, { instant: true });
+  }).observe(modeToggleEl);
+}
+
+// Reposition highlight when document direction changes (RTL locale switch)
+new MutationObserver(() => {
+  requestAnimationFrame(() => {
+    const activeBtn = modeToggleEl?.querySelector('.mode-btn.active');
+    if (activeBtn) positionModeHighlight(activeBtn, { instant: true });
+  });
+}).observe(document.documentElement, { attributes: true, attributeFilter: ['dir'] });
 
 // --- Stop / Abort ---
 
diff --git a/src/firefox/styles/sidepanel.css b/src/firefox/styles/sidepanel.css
index 79de06e44..a11e2c131 100644
--- a/src/firefox/styles/sidepanel.css
+++ b/src/firefox/styles/sidepanel.css
@@ -1983,10 +1983,37 @@ body {
   border: 1px solid var(--border);
   border-radius: 8px;
   padding: 2px;
+  position: relative;
+}
+
+.mode-toggle-highlight {
+  position: absolute;
+  top: 2px;
+  left: 0;
+  z-index: 0;
+  height: calc(100% - 4px);
+  border-radius: 6px;
+  background: var(--accent-dim);
+  pointer-events: none;
+  will-change: transform, width;
+  transition:
+    transform 170ms cubic-bezier(0.22, 1, 0.36, 1),
+    width 170ms cubic-bezier(0.22, 1, 0.36, 1),
+    background 170ms ease;
+}
+
+.mode-toggle-highlight.act {
+  background: rgba(255, 152, 0, 0.12);
+}
+
+.mode-toggle-highlight.instant {
+  transition: none;
 }
 
 .mode-btn {
   flex: 1;
+  position: relative;
+  z-index: 1;
   background: none;
   border: none;
   color: var(--text-muted);
@@ -1995,7 +2022,7 @@ body {
   padding: 5px 0;
   border-radius: 6px;
   cursor: pointer;
-  transition: all 0.2s;
+  transition: color 0.2s;
   text-align: center;
 }
 
@@ -2004,12 +2031,10 @@ body {
 }
 
 .mode-btn.active {
-  background: var(--accent-dim);
   color: var(--accent);
 }
 
 .mode-btn.active.act {
-  background: rgba(255, 152, 0, 0.12);
   color: var(--warning);
 }