Bug 978084 - Make sure @customizing-movingItem gets removed by ensuring dragend gets fired. r=Gijs

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extra : rebase_source : 7e590a535947230f62fbbe6e0aee407379c86e5e
Bug 958043 - Remove useless enable-content-actors pref and ContentTabActor in b2g parent process. r=past

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extra : rebase_source : bae30ce729a4d50de581365547b23b719a672171