This weekend I found that typing into any text box on my Firefox browser resulted in Greek characters. I had to copy and paste from Notepad in order to get anything done. Restarting Firefox did not do any good. The problem went away after I restarted Logos.
This is likely to be a Firefox problem, but I thought that since it seems to be coupled to Logos, I would mention it here.
Firefox: 38.0.5; Windows 7
Logos 6.3 SR-2