Until yesterday, my MATE desktop had the names of three menus at the top left, between a little Ubuntu logo and the Firefox icon, reading "Applications Places System." Yesterday they disappeared.
I didn't use "Places" much, but I waas missing "Applications" and "System." Well, apparently I have managed to get the two of the menu contents back in a way, with a double circle and an arrow head with "Menu" to the right. And I managed to "Applications" and "Systems" combined in a single menu called "Main Menu" marked with a variation of the Ubuntu logo, so no problem, but I remain surprised. What in the world led to this? Did I do something dumb?