All platforms. Bug 866104 is my most likely target, appears to come from the range: <http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=c80dc6ffe865&tochange=81dd97739fa1>. https://tbpl.mozilla.org/php/getParsedLog.php?id=22939924&tree=Thunderbird-Trunk
Created attachment 750604 [details] [diff] [review] The fix Ok, it was actually bug 869209 that caused this - as social is now pulling in places in its tests and Thunderbird disables places by default. Therefore we need to include enabling of places to get the test to pass. This works for me locally.