If there's a single app that defines the OS X experience, it's probably Safari. Not everyone uses it (many of my friends and family members prefer Chrome), but as the default browser it's the window on the Web for most Mac users. I've been using an early developer preview of Yosemite for the past few weeks, and it's clear that Safari is the stock Apple app that will change the most when users install OS X Yosemite upon its arrival this fall.
Where's the rest of me?
By default, Safari is sparsely decorated in Yosemite. There's no longer a title bar with the name of webpages, and the "stoplight" window buttons have merged down into the toolbar as they have in some other apps. All other toolbars are off by default, and the address/search bar no longer even displays a full URL, just the name of the host that's serving the page you're viewing. (If you want to see the name of the page you're on, you need to have the Tab Bar open — tabs are the only place that display page names.)
The result is a minimalist look that feels like it was taking right out of Safari on iOS 7: One bar, very little text, and everything else is the webpage itself. On a phone, minimizing the stuff around the webpage is desperately necessary. On a tablet it's a good idea. On a 15-inch Retina MacBook Pro or a 27-inch iMac it feels a little pointless.
The way Safari does things in Yosemite is essentially the opposite of the way I use my Web browser. The good news is, most of these choices can simply be changed by the judicious use of the View menu, which can restore the Favorites Bar (which, oddly, now centers the bookmarks!) and Status Bar. Unfortunately, the page name doesn't show up in the menu bar anymore, nor can you opt to see the full webpage URL.
General crankiness aside, there's also a major usability problem with this design approach. By removing the Title Bar space at the top of the browser window, Safari windows are immediately more difficult to drag around the screen. The center of the window is now the Address/Search Bar, and you can't click on that. Nor can you click on the "stoplight" buttons or any of the other toolbar buttons. There is a narrow gray space just to the left and right of the Address/Search Bar, and that's the only place from which you can drag reliably.
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