## Environment - revision: https://hg.mozilla.org/mozilla-central/rev/076a7a66096f9e8d102548397254be32eb26bc3d - Build ID: 20170501030204 - OS: macOS Sierra 10.12.4 ## Step to Reproduce 1. Select a word in a page. 2. Tap with 3 fingers. ## Expected Result - Open a QuickLook popup Dictionary for selected word with some result. ## Actual Result - Open a QuickLook popup. - But the popup is empty if I selected "Hello" or other popular words. - I confirm the following error in Console.app ``` LookupViewService (Foundation) <NSXPCConnection: 0x60000011d760> connection from pid 69427: Warning: Exception caught during decoding of received message, dropping incoming message. Exception: Exception while decoding argument 0 (#2 of invocation): <NSInvocation: 0x6000002607c0> return value: {v} void target: {@} 0x0 selector: {:} bootstrap:withReply: argument 2: {{?=@@@@{CGRect={CGPoint=dd}{CGSize=dd}}ccc@@@I}} <00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000> argument 3: {@?} 0x0 (block) Exception: decodeObjectForKey: class "TitlebarAndBackgroundColor" not loaded or does not exist ``` ## Additional Information - I confirm this problem is reproducible on Firefox 54.0b3 (https://hg.mozilla.org/releases/mozilla-beta/rev/0b1c079a2a4b826b217ec7d3c7446ef942e4fc0e)

I don't remember when I confirm this regressions at first. But I feel this problem happens from 1~2 week ago.