When I use firefox with windows8.1, I can't use backspace and delete key for deleting characters. Furthermore, I can't input any alphabet into the input screen of firefox.(Now this sentence is inputted by Chrome) Only full-width alphabet (ＬＩＫＥ　ＴＨＩＳ) and Japanese(このように) I can input, and that characters I inputted CAN'T be deleted, by using backspace or delete key. I shut down firefox and my PC, and I also reset firefox, but this problem is still existing. Please solve this problem.