Created attachment 8829246 [details] ff-element-duplicated.gif Steps to Reproduce: 1. Paste the following Data URI into your address bar: data:text/html;charset=utf-8,<x-foo contenteditable><div>ab</div><p>cd</p></x-foo> 2. Place the cursor before "b" and select through "c" so that both letters are selected 3. Press backspace Expected Results: <x-foo contenteditable> <div>ad</div> </x-foo> Actual Results: <x-foo contenteditable> <div>a</div> </x-foo> <x-foo contenteditable> <p>d</p> </x-foo> Additional details: Enabling dom.webcomponents.customelements.enabled and registering the element with document.registerElement has no affect. The same problem is reproducible using <span contenteditable> as the containing element (instead of <x-foo contenteditable>) so I suspect Firefox treats the contained elements as invalid block children of an inline parent. Styling the container with "display:block;" doesn't help, and in either case the contenteditable element should not be duplicated.
Status: UNCONFIRMED → NEW
Ever confirmed: true
Priority: -- → P3
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