diff --git a/src/core/bar_helper.py b/src/core/bar_helper.py
index 37f882e9..d4a587d3 100644
--- a/src/core/bar_helper.py
+++ b/src/core/bar_helper.py
@@ -37,7 +37,12 @@
 from core.utils.win32.bindings import SetWindowPos
 from core.utils.win32.bindings.user32 import KillTimer, RegisterWindowMessage, SetTimer, user32
 from core.utils.win32.structs import MSG
-from core.utils.win32.utilities import apply_qmenu_style
+from core.utils.win32.utilities import (
+    apply_qmenu_style,
+    is_process_fullscreen_on_monitor,
+    is_window_fullscreen,
+    is_window_maximized,
+)
 
 # Register TaskbarCreated message to detect Explorer restarts
 WM_TASKBARCREATED = RegisterWindowMessage("TaskbarCreated")
@@ -551,6 +556,19 @@ def _is_foreground_excluded(self) -> bool:
                 self.EXCLUDED_WINDOW_CLASS_SUFFIXES
             ):
                 return True
+            if is_window_fullscreen(hwnd):
+                if is_window_maximized(hwnd):
+                    # Maximized windows cover the screen but are not fullscreen apps
+                    return True
+                # True fullscreen (not maximized) allow hiding the bar
+                return False
+            # Foreground not fullscreen check if a sibling window from the
+            # same process is fullscreen (e.g. Firefox HTML5 fullscreen video)
+            process_fs = is_process_fullscreen_on_monitor(
+                hwnd, self.EXCLUDED_WINDOW_CLASSES, self.EXCLUDED_WINDOW_CLASS_SUFFIXES
+            )
+            if not process_fs:
+                return True
         except Exception:
             pass
         return False
diff --git a/src/core/utils/win32/utilities.py b/src/core/utils/win32/utilities.py
index e01abbe4..c4cb00a3 100644
--- a/src/core/utils/win32/utilities.py
+++ b/src/core/utils/win32/utilities.py
@@ -7,6 +7,7 @@
 
 import win32api
 import win32gui
+import win32process
 from PyQt6.QtGui import QCursor
 from PyQt6.QtWidgets import QApplication, QWidget
 from win32api import GetMonitorInfo, MonitorFromWindow
@@ -281,6 +282,63 @@ def is_window_maximized(hwnd: int) -> bool:
     return window_placement[1] == SW_MAXIMIZE
 
 
+def is_window_fullscreen(hwnd: int) -> bool:
+    """Check if a window covers the entire monitor it is on."""
+    if win32gui.IsIconic(hwnd):
+        return False
+    rect = GetWindowRect(hwnd)
+    monitor_info = GetMonitorInfo(int(MonitorFromWindow(hwnd)))
+    mon = monitor_info["Monitor"]  # (left, top, right, bottom)
+    return rect[0] <= mon[0] and rect[1] <= mon[1] and rect[2] >= mon[2] and rect[3] >= mon[3]
+
+
+def is_process_fullscreen_on_monitor(
+    hwnd: int,
+    excluded_classes: set[str] | None = None,
+    excluded_suffixes: tuple[str, ...] | None = None,
+) -> bool:
+    """Check if any visible window belonging to the same process as hwnd
+    is fullscreen on the same monitor. This should handles apps like Firefox
+    that use a separate child window for HTML5 fullscreen video."""
+    try:
+        _, target_pid = win32process.GetWindowThreadProcessId(hwnd)
+        if target_pid == 0:
+            return False
+
+        target_monitor = int(MonitorFromWindow(hwnd))
+        _excluded_classes = excluded_classes or set()
+        _excluded_suffixes = excluded_suffixes or ()
+        found = False
+
+        def _enum_cb(candidate_hwnd, _):
+            nonlocal found
+            try:
+                if not win32gui.IsWindowVisible(candidate_hwnd):
+                    return True
+                _, c_pid = win32process.GetWindowThreadProcessId(candidate_hwnd)
+                if c_pid != target_pid:
+                    return True
+                cls = GetClassName(candidate_hwnd)
+                if cls in _excluded_classes or cls.endswith(_excluded_suffixes):
+                    return True
+                if int(MonitorFromWindow(candidate_hwnd)) != target_monitor:
+                    return True
+                if is_window_fullscreen(candidate_hwnd):
+                    found = True
+                    return False
+            except Exception:
+                pass
+            return True
+
+        try:
+            win32gui.EnumWindows(_enum_cb, 0)
+        except Exception:
+            pass
+        return found
+    except Exception:
+        return False
+
+
 def get_hwnd_info(hwnd: int) -> dict:
     with suppress(Exception):
         monitor_hwnd = get_monitor_hwnd(hwnd)