"Toogle file browser button" not easily discoverable

The icon and placement of the new "Toogle file browser button" in 11.4.5-ee is such that I was unable to figure out how to disable the file browser without searching the bug tracker. (This was somewhat urgent, as the file browser reduces usability significantly on laptops with 1200x800 screens.)

There should be a 'close' button in the usual location, or a way to drag the divider to reduce its real estate. The current hamburger menu button does have a mouseover that reveals its purpose, but is otherwise unintuitive and nondiscoverable for this user.