Compare the favicon of abput:firefox *in the tabs tray* in Nightly and Beta - it should be a tiny Firefox logo, but on Nightly it's currently missing and replaced by a "?" because Snorp broke it.
Bug 1517160 Comment 6 Edit History
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Compare the favicon of about:firefox *in the tabs tray* in Nightly and Beta - it should be a tiny Firefox logo, but on Nightly it's currently missing and replaced by a "?" because Snorp broke it.