In version 74. I linked this to illustrate, that features for users are made hastily, as if by "intern", to check the box and get paid. I cannot imagine a job or a student project where I was tasked to make keyboard shortcuts editor and got away with implementation that lacked ability to delete shortcut. But I get it. Since Firefox is for free, I have to either a) shut up, or b) hail it positively. There's no room for negative feedback.