"Win10 Firefox safe mode?" over in Malware, should be over here in Internet/Browsers?
 

Title is the message

Shirley, seeing you used CCleaner to remove Firefox, you have probably damaged it by removing the registry entries and leaving the rest of it there, and I'm not sure of the best way to approach this, but I'd try removing it using: Start/Settings/Apps and then downloading and reinstalling it.

Others may have a better approach, see any suggestions before starting.