Firefox Sidebar Still Visible After Checking “Hide Tabs and Sidebar”?

TLDR

Select the hiding option, then click the sidebar button to hide the visible strip.
Collapsing the strip, hiding it and switching to horizontal tabs are separate actions.
The legacy sidebar setting in Firefox 157 also disables native vertical tabs.

The hiding option still needs a button click

If you enabled vertical tabs and checked “Hide tabs and sidebar,” but the icons remain visible, click the sidebar button in the browser toolbar. Selecting the option and hiding the currently visible strip are separate steps.

A September 30 support question from a Firefox 157 user describes exactly this confusion. The user expected the checkbox to hide everything until the pointer reached the edge. They later marked the question solved after discovering the top-left button that opens and closes the sidebar.

Open Customize sidebar with the gear at the bottom of the sidebar.
Select Hide tabs and sidebar.
Click the toolbar’s sidebar button to hide it. Click that button again to bring it back.

Mozilla’s sidebar guide documents hiding as a way to reclaim room while using vertical tabs. If you expected automatic reveal on hover, first distinguish that behavior from explicitly opening and closing the strip.

Collapsed icons are not the same as a hidden sidebar

Firefox maintains separate expanded, collapsed and hidden states. Tab orientation and the tools shown in the sidebar are separate settings too. That distinction explains why removing tab titles can leave an icon column behind.

Your goal	Relevant action	What changes
Use a narrower tab strip	Collapse the vertical sidebar	Icons remain in a compact view.
Keep vertical tabs but clear the side of the window	Select the hiding option, then click the sidebar button	The tab strip and sidebar are hidden.
Put tabs along the top again	Turn off vertical tabs in customization or the toolbar/tab-strip context menu	The tab layout changes.
Remove one tool icon	Uncheck that tool in sidebar customization	Only that tool leaves the displayed selection.

Choose based on which part is taking up unwanted space. Hiding preserves your choice of vertical tabs; changing tab orientation solves a different problem.

Restoring the legacy sidebar also turns off vertical tabs

Firefox 157 enabled the updated sidebar for everyone and removed the old Show sidebar option from Settings. Instructions pointing to that checkbox can therefore lead you to a control that is no longer there.

The release notes still provide a way back to the previous sidebar:

Enter about:config in the address bar.
Continue past the confirmation screen if it appears, then search for sidebar.revamp.
If its value is true, use the toggle or double-click the preference to change it to false.

This disables Firefox’s native vertical tabs as well. Mozilla says the preference will remain available through the end of 2027. To return a changed preference to its default, use the configuration editor’s Reset control.

Keep the new sidebar if hiding is all you need

For more document space while retaining vertical tabs, use the hiding option and toolbar button. For tabs at the top, change orientation. Restore the legacy sidebar when you want that older interface and accept losing native vertical tabs with it.