On Windows, I can hit Ctrl + Alt + Delete and kill apps or do other stuff. Sometimes Firefox browser hangs on macOS. Is there an equivalent of Ctrl + Alt + Delete keyboard shortcut to kill frozen apps on Apple macOS Sierra?

There is no all in one equivalent on macOS. Yes, if your app on Mac computer stops working and you cannot quit the app such as Firefox generally, use Force Quit to close that app.

How to force an app to quit on mac os

To start Force Quit app, click on the Apple menu and select Force Quit:

Or you can use keyboard shortcut. Press Command-Option-Esc to bring Force Quit app:

Select the app such as Firefox in the Force Quit window, then click Force Quit.

Say hello to Activity Monitor

The closest similar of the Windows Task Manager is The Activity Monitor app. It shows the processes that are running on your computer and much more. To start the Activity Monitor:

1. Press Command–space on your keyboard
2. Start typing activity monitor
3. As soon as activity monitor is displayed, hit enter key.