This happens occasionally, and I'm not sure if there is a consistent cause: I get an error message saying something like: "An error has occurred. Please restart Firefox." This latest time I had not actually touched the keyboard for at least five seconds. The screen flashed, which it has started doing from time to time -- it seems to be when I have made an entry in the Notes in the right-hand column, perhaps it is saving it. Then the Zotero data part of the screen went blank except for the error message. Report ID 1900703441.