It seems Mozilla is doing what they've always done: look at features that work, and then integrate them into Firefox. Currently, the Chrome interface seems to work well, so they're porting it in - however, that's the default. Contrary to other browsers, at least Firefox allows you to change your interface - and while I, personally, enjoy opening a dozen tabs at once, many people I know don't go past 2 or 3 - as such, the major UI feature I appreciate is the ability to have the tabs on a menu bar with other stuff. And, if Mozilla is consistent, if you've set up your interface differently from default, the update won't break it. As for silent updates, they'll be enabled by default but making them manual again is a checkbox away.