Minisize

A tiny browser living in your Menubar.

Available on the Mac App Store Minisize requires Mac OS X 10.7 or higher.

http://mediaqueri.es

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Orientation

Tilt the app window to mimic portrait and landscape mode. Use ⌘ + F or the icon to activate.
Bookmarks

Manage your favorite sites and web apps right from the navigation bar or via Settings.
Keyboard Shortcuts

Use your keyboard to navigate through the app. Check out the available shortcuts.
User Agents

Debug your responsive designs across devices. Check out our recommended User Agents.
Global Hotkey

Choose your hotkey via settings and toggle the app window from anywhere on you Mac.
Float on top

Minisize can now float above all open windows. It results in rapid development.

Safari iOS 5.0 iPhone Mozilla/5.0 (iPhone; CPU iPhone OS 5_0 like Mac OS X) AppleWebKit/534.46 (KHTML, like Gecko) Version/5.1 Mobile/9A334 Safari/7534.48.3
Safari 5.1.5 Mac Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_3) AppleWebKit/534.55.3 (KHTML, like Gecko) Version/5.1.5 Safari/534.55.3
Chrome 18.0 Mac Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_3) AppleWebKit/535.19 (KHTML, like Gecko) Chrome/18.0.1025.168 Safari/535.19
Firefox 9.0 Mac Mozilla/5.0 (Macintosh; Intel Mac OS X 10.6; rv:9.0) Gecko/20100101 Firefox/9.0

For more UAs check out: useragentstring.com.