diff --git a/src/renderer/src/RightAssistantSidebar.resize.test.tsx b/src/renderer/src/RightAssistantSidebar.resize.test.tsx
index 8b4b4394..7cbf6888 100644
--- a/src/renderer/src/RightAssistantSidebar.resize.test.tsx
+++ b/src/renderer/src/RightAssistantSidebar.resize.test.tsx
@@ -276,17 +276,26 @@ describe('RightAssistantSidebar resizing', () => {
       screen.getByRole('button', { name: '全屏显示浏览器' })
     )
     expect(sidebar).toHaveClass('assistant-sidebar--browser-fullscreen')
+    expect(
+      sidebar.style.getPropertyValue('--assistant-sidebar-width')
+    ).toBe('420px')
     expect(
       screen.getByRole('button', { name: '退出浏览器全屏' })
     ).toHaveAttribute('aria-pressed', 'true')
     expect(
       screen.getByRole('separator', { name: '调整助手工作栏宽度' })
-    ).toHaveAttribute('aria-disabled', 'false')
+    ).toHaveAttribute('aria-disabled', 'true')
+    expect(
+      screen.getByRole('separator', { name: '调整助手工作栏宽度' })
+    ).toHaveAttribute('tabindex', '-1')
 
     fireEvent.keyDown(window, { key: 'Escape' })
     expect(sidebar).not.toHaveClass(
       'assistant-sidebar--browser-fullscreen'
     )
+    expect(
+      sidebar.style.getPropertyValue('--assistant-sidebar-width')
+    ).toBe('420px')
   })
 
   it('keeps the docked sidebar non-modal', () => {
diff --git a/src/renderer/src/RightAssistantSidebar.tsx b/src/renderer/src/RightAssistantSidebar.tsx
index a727b4bd..13b67763 100644
--- a/src/renderer/src/RightAssistantSidebar.tsx
+++ b/src/renderer/src/RightAssistantSidebar.tsx
@@ -234,6 +234,10 @@ function measureSplitLayoutWidth(
   if (!sidebar || !workspace) {
     return fallbackWidth
   }
+  const layoutWidth = sidebar.parentElement?.getBoundingClientRect().width ?? 0
+  if (layoutWidth > 0) {
+    return layoutWidth
+  }
   const measuredWidth =
     workspace.getBoundingClientRect().width +
     sidebar.getBoundingClientRect().width
@@ -698,7 +702,6 @@ export function RightAssistantSidebar({
   )
   const [isResizing, setIsResizing] = useState(false)
   const [browserFullscreen, setBrowserFullscreen] = useState(false)
-  const browserRestoreRatio = useRef(sidebarRatio)
   const sidebarRef = useRef<HTMLElement>(null)
   const wasOpen = useRef(false)
   const sidebarWidth = clampSidebarWidth(
@@ -804,9 +807,12 @@ export function RightAssistantSidebar({
     }),
     []
   )
+  const browserFullscreenActive =
+    open && activeWorkbarApp === 'browser' && browserFullscreen
   const sidebarWidthLimits = getSidebarWidthLimits(splitLayoutWidth)
   const canResize =
     open &&
+    !browserFullscreenActive &&
     sidebarWidthLimits.maximum > sidebarWidthLimits.minimum
   const topLevelTasks = useMemo(
     () => tasks.filter((task) => !task.parentTaskId),
@@ -853,26 +859,9 @@ export function RightAssistantSidebar({
     }
   }, [tab, workbarInstances])
 
-  const browserFullscreenActive =
-    open && activeWorkbarApp === 'browser' && browserFullscreen
   const toggleBrowserFullscreen = useCallback((): void => {
-    if (browserFullscreen) {
-      setSidebarRatio(browserRestoreRatio.current)
-      setBrowserFullscreen(false)
-      return
-    }
-    const layoutWidth = measureSplitLayoutWidth(
-      sidebarRef.current,
-      splitLayoutWidth
-    )
-    browserRestoreRatio.current = sidebarRatio
-    setSidebarRatio(
-      layoutWidth > 0
-        ? getSidebarWidthLimits(layoutWidth).maximum / layoutWidth
-        : sidebarRatio
-    )
-    setBrowserFullscreen(true)
-  }, [browserFullscreen, sidebarRatio, splitLayoutWidth])
+    setBrowserFullscreen((current) => !current)
+  }, [])
 
   useEffect(() => {
     if (!browserFullscreenActive) {
diff --git a/src/renderer/src/WorkspacePrimitives.test.tsx b/src/renderer/src/WorkspacePrimitives.test.tsx
index b3df9909..a16b1982 100644
--- a/src/renderer/src/WorkspacePrimitives.test.tsx
+++ b/src/renderer/src/WorkspacePrimitives.test.tsx
@@ -244,6 +244,9 @@ describe('WorkspacePrimitives', () => {
     expect(stylesheet).toMatch(
       /\.assistant-sidebar--open\s*\{[^}]*width:\s*var\(--assistant-sidebar-width,\s*30%\);[^}]*flex-basis:\s*var\(--assistant-sidebar-width,\s*30%\);/u
     )
+    expect(stylesheet).toMatch(
+      /\.assistant-sidebar--browser-fullscreen\s*\{[^}]*position:\s*absolute;[^}]*z-index:\s*4;[^}]*width:\s*100%;[^}]*inset:\s*0;/u
+    )
     expect(stylesheet).not.toMatch(
       /@media \(max-width: 719px\)\s*\{(?:[^{}]|\{[^{}]*\})*?\.assistant-sidebar/u
     )
diff --git a/src/renderer/src/styles.css b/src/renderer/src/styles.css
index c9f62bcb..3f9e8586 100644
--- a/src/renderer/src/styles.css
+++ b/src/renderer/src/styles.css
@@ -3823,6 +3823,12 @@ button > svg {
 }
 
 .assistant-sidebar--browser-fullscreen {
+  position: absolute;
+  z-index: 4;
+  width: 100%;
+  border-left-width: 0;
+  flex-basis: 100%;
+  inset: 0;
   transition: none;
 }
 
@@ -3847,6 +3853,10 @@ button > svg {
   display: block;
 }
 
+.assistant-sidebar--browser-fullscreen > .assistant-sidebar__resize-handle {
+  display: none;
+}
+
 .assistant-sidebar__resize-handle::after {
   position: absolute;
   top: 0;