Bug 1009530 - [User Story] Visual to indicate when in edit mode

https://bugzilla.mozilla.org/show_bug.cgi?id=1009530

Ok, TBH I generally prefer ease-in for most movement animations, but for opacity animations I really wasn't sure if it mattered. It seemed to me like linear might be better, but I'll go ahead and update it to ease-in. The background one is only really there to delay the slight change in color.