Hi

If you select the cog wheel icon at the bottom of the sidebar launcher, you should see an option to "Show and hide sidebar". Selecting this will hide the sidebar.

It did not delete the sidebar.

Hi, did you select the "Show and hide" option for the Sidebar button? With that setting, when you close the current sidebar, the vertical button bar should be removed, too.

However, that setting does not remove the vertical button bar when the sidebar is open. Is that the problem?

I only have the cogs icon and I have selected Expand/Collapse and Show/Hide. I cannot get it to go away. It is consuming screen space.

After selecting Show/Hide, you can use the Sidebars button on the toolbar to close the sidebar. I think when this vertical button bar design was turned on, the Sidebars button was added to the left part of the toolbar, near the reload button. If needed, you can add it yourself from the Customize panel. See: Customize Firefox controls, buttons and toolbars.