Permanently remove sidebar that pops up

I have never seen that happen and I can't find anything in the Preferences, menus, or even the Develop menu that would cause that behavior.

Ok, I just thought, "how could someone see something I've never seen," then I remembered the stupid Full Screen thing, which I never use. Put it in Full Screen, hovered over the left side of the window--bam, there popped out the sidebar.

Simple solution, don't use Full Screen view. Otherwise, I can't find a way to disable it.

[Edited by Moderator]

I've never heard of that. I have to click on the Sidebar button or use the View menu to make it show.

Is it the standard Safari Sidebar with Bookmarks, reading pane, and history? If not, maybe an extension you installed.

I don't see anything in the Preferences or menus.