I'm using GNOME, dunno if this also happens in other desktop environments but I'm guessing it does. The attached picture shows what happens right after I click a pinned Nightly icon/shortcut. A new window is opened, labeled "Firefox" by GNOME Shell and using the standard Firefox icon, even though it's actually Nightly (says so on the titlebar and the About window). This is not a major issue but it's fairly irritating and seems like something I should be able to fix easily.