• A lot of browser improvements are in the Opera Tweaks section.

...but, more general browsing improvements include:

Tab/Bookmark Fusion

Media Player

Any audio or video that's playing in the browser can be controlled through a mini-player.

• Global hotkeys
• Media metadata (from public federated server)
• History
• System tray info
• Tray Alerts
• Coordination
  • Make sure two windows can't play media at the same time

/!\ TODO: Aggregate notes on browser improvements and scan them in.