Bugzilla

_As of 2025-12-23:_

**This issue is not a user configuration problem but a recurring regression in Firefox’s Windows window-state handling.**
On Windows 10, when the taskbar is set to auto-hide and Firefox is launched or used in a maximized window (not F11 fullscreen), the taskbar frequently fails to reappear on mouse hover at the bottom edge of the screen. This does not occur with other applications under the same conditions.
The problem is intermittent and highly dependent on window state transitions (launch state, restore, maximize, snap, focus changes), which strongly suggests incorrect interaction between Firefox’s maximized window behavior and Windows fullscreen heuristics.
Pressing **F11 repeatedly** (entering and exiting fullscreen) can **sometimes** cause the taskbar to reappear, but this behavior is inconsistent and clearly not a valid or reliable solution. The fact that fullscreen toggling temporarily affects the outcome further indicates a window state misclassification.
Multiple users (including myself) confirm that:
– The issue persists across several Firefox versions and reappears after being “fixed”.
– Changing widget.windows.fullscreen_marking_method may work temporarily for some users but is not a reliable or permanent solution.
– about:config or user.js workarounds do not consistently resolve the issue.
– Minimizing/restoring or snapping the window temporarily restores taskbar access, confirming a window-state detection problem rather than a taskbar bug.
This behavior effectively breaks a standard Windows feature (taskbar auto-hide) and should not be considered an edge case. The root cause appears to be Firefox incorrectly triggering Windows fullscreen detection for maximized windows under certain conditions.
This issue has existed in various forms for years and remains unresolved in current versions.
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_Tested on:_
- Firefox 146.0.1 (64-bit)
- Windows 10 Pro 22H2 (OS Build 19045.3448)
- Windows Feature Experience Pack 1000.19044.1000.0
- NVIDIA Studio Driver 591.44
System:
- Intel i9-9900K
- NVIDIA RTX3090

_As of 2025-12-23:_

**This issue is not a user configuration problem but a recurring regression in Firefox’s Windows window-state handling.**

On Windows 10, when the taskbar is set to auto-hide and Firefox is launched or used in a maximized window (not F11 fullscreen), the taskbar frequently fails to reappear on mouse hover at the bottom edge of the screen. This does not occur with other applications under the same conditions.

The problem is intermittent and highly dependent on window state transitions (launch state, restore, maximize, snap, focus changes), which strongly suggests incorrect interaction between Firefox’s maximized window behavior and Windows fullscreen heuristics.
Pressing **F11 repeatedly** (entering and exiting fullscreen) can **sometimes** cause the taskbar to reappear, but this behavior is inconsistent and clearly not a valid or reliable solution. The fact that fullscreen toggling temporarily affects the outcome further indicates a window state misclassification.

Multiple users (including myself) confirm that:
– The issue persists across several Firefox versions and reappears after being “fixed”.
– Changing widget.windows.fullscreen_marking_method may work temporarily for some users but is not a reliable or permanent solution.
– about:config or user.js workarounds do not consistently resolve the issue.
– Minimizing/restoring or snapping the window temporarily restores taskbar access, confirming a window-state detection problem rather than a taskbar bug.

This behavior effectively breaks a standard Windows feature (taskbar auto-hide) and should not be considered an edge case. The root cause appears to be Firefox incorrectly triggering Windows fullscreen detection for maximized windows under certain conditions.
This issue has existed in various forms for years and remains unresolved in current versions.

---

_Tested on:_
- Firefox 146.0.1 (64-bit)
- Windows 10 Pro 22H2 (OS Build 19045.3448)
- Windows Feature Experience Pack 1000.19044.1000.0
- NVIDIA Studio Driver 591.44
System:
- Intel i9-9900K
- NVIDIA RTX3090