Small Patch for Firefox

A user brought an issue on Firefox to my attention about a month ago. The single quote (') and forward slash (/) trigger the search bar on Firefox, and the game loses focus, so it never registers the release of these keys. Since I didn't have time to investigate how to block these events on Firefox, I opted to remove these keys from the game as they aren't essential to the experience. I also removed back tick (`) and back slash (\) to avoid confusion.

Thanks again to thePalindrome for letting me know.