Pretty consistent. I haven't timed it, but it certainly feels like more than 15 seconds for my 50-100 tabs. I'm not in quite as pure of a situation as that benchmark though-- I have plenty of other programs using memory and I'm waiting for the page to actually render. During some of my Firefox launches lately I also had a bunch of other applications launching at the same time since I was trying to debug a WebGL page that sporadically hangs/reboots my machine (in both Firefox and Chrome)