PS: I just ran a diff on about:support, comparing Mozilla's and TW's build. Config seems exactly the same: diff mozillabuild.txt twbuild.txt 7d6 < Update Channel: release 167c166 < dom.push.userAgentID: 0cb13890125c405ebfc0b752dd3fdf9c --- > dom.push.userAgentID: 1a53a2af73374dfea303607f17ab448a 172,173c171,172 < security.sandbox.content.tempDirSuffix: b302fa80-775c-4ee1-8343-2a28d5c6f794 < security.sandbox.plugin.tempDirSuffix: e0120e53-f70b-484a-8d73-d1c0fd06a217 --- > security.sandbox.content.tempDirSuffix: 269201ae-9c87-46c2-a716-afb815eb7e1b > security.sandbox.plugin.tempDirSuffix: 3e842a6a-a45d-494e-b431-51059e5cbd35 238,240c237,239 < App Locales: ["en-US"] < Regional Preferences: ["en-US"] < Default Locale: "en-US" --- > App Locales: ["en-US","und"] > Regional Preferences: ["en-US","und"] > Default Locale: "und"