UK guy:
I'm sure they appreciate your honesty, however, depending on why and what the whole story is easyjet might not have a choice because of safety and security reasons.
In general they seem to give people a chance but some things are worse than others and if there is the slightest suspicion that your history suggest trouble for your colleagues/passengers/the safety of an aircraft they won't take the chance just to do you a favour.
I hope it's nothing so severe and I hope you'll be ok as you sound like you have learned from your mistake whatever it was. Good luck!
I wouldn't try to hide it from them because you never know who knows whom and if it ever comes to light you'll be in even more trouble and would probably have a second bad reference to deal with.
I think they are not allowed to give a bad reference as such but they are allowed to give your reason for leaving and if that's gross misconduct they will say so. Any chance you can talk to your old company and get them to change it?