Fix
On Firefox 153 (currently in beta) the amber outline that marks the active pane in a split view stopped closing along its bottom edge. Firefox 153 restructured split view so each pane's footer now lives inside the content area, which together with FoxOne's edge-to-edge content left the pane sitting flush against the window's bottom edge and clipped the outline there. FoxOne now keeps a small inset at the bottom of each split pane, so the active-pane outline closes cleanly on all four sides again. Firefox 152 and earlier were never affected.