After first enabling the feature, I've been unable to disable it again. That includes hitting the "Restore all default settings (in all sections)" button, and ensuring that all of the features under the Beta section are unchecked. I still see "Edit Source" when I go to edit, and am prompted about the visual editor. Any ideas?
Browser: Firefox
OS: Windows10
Wiki Skin: Vector
Update: even more interesting! The "Edit Source" option has disappeared, and I am no longer prompted. Wiki highlighting isn't coming up. Seems like there was some kind of delay.
Update 2: Wiki highlighting still isn't coming up. Attempted to remedy by closing reopening browser and logging out/in of Wikipedia. Problem persists.
Update 3: Resolved! It looks like hitting that initial restore default also turned off the syntax highlighter gadget! How easy it is to take little things like that for granted. So, the only real issue was the delay between the disabling of the feature.