Dashboard disappears after updating or saving

I never encountered this before, maybe some of you have.
When I edit a page or change a setting in the Dashboard, then click the update button, the Dashboard disappears. I can bring it back by hitting the back button on my browser, but that cancels the update. I can go to my bookmarks to reconnect to the Dashboard, but that is inconvenient.
In Firefox, the Dashboard won’t open at all. Instead, I get a blank page with this ??? in the top left corner. This symbol also flashed for a very short time in other bowsers when I hit the update button.
Has anyone encountered this before? Any ideas are appreciated.