Bug 1699506 introduced the pref `full-screen-api.macos.shiftToolbar`. When true, the toolbar shifts down when the user mouses to the top of the screen in fullscreen mode. It does this by using the `NSTitlebarAccessoryViewControllerAPI`. The pref is false by default because it draws a 1px flickering white line at the top of the window. QA found in bug 1699506 comment 14 that only macOS 11+ gets the flickering line. mstange found that the line is only drawn when the Firefox window is drawn with the regular Aqua appearance. If `widget.macos.respect-system-appearance` is true and the system is in Dark mode (and thus Firefox is drawn with the Aqua Dark appearance), the line is not drawn. I suspect this issue is closely related to bug 1578634, so I'm marking that as a dependency.
Bug 1700211 Comment 0 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
Bug 1699506 introduced the pref `full-screen-api.macos.shiftToolbar`. When true, the toolbar shifts down when the user mouses to the top of the screen in fullscreen mode. It does this by using the `NSTitlebarAccessoryViewController` API. The pref is false by default because it draws a 1px flickering white line at the top of the window. QA found in bug 1699506 comment 14 that only macOS 11+ gets the flickering line. mstange found that the line is only drawn when the Firefox window is drawn with the regular Aqua appearance. If `widget.macos.respect-system-appearance` is true and the system is in Dark mode (and thus Firefox is drawn with the Aqua Dark appearance), the line is not drawn. I suspect this issue is closely related to bug 1578634, so I'm marking that as a dependency.