TabView looks like the biggest new feature in the next Safari. It borrows the tab view from the iOS version of Safari, allowing users to zoom out and see all live tabs with thumbnails. The trackpad can then be used to scroll through the open tabs.
The new version of Safari will keep tabs in sync. In addition those tabs will sync over iCloud with your other devices.
Next to the back and forward buttons there is a new Cloud button that drops down a new menu that shows search results from bookmarks and history. The new unified search bar in Safari will find hits in browsing history, your bookmarks and tabs.
The unified search mimics what Chrome and Firefox users enjoy, allowing users to type both searches and URL addresses into the same box.
Here’s a full list list of Mountain Lionfeatures from earlier this year.