Sometimes you can run a piece of code, click an action, just generally do something a bit heavier than you expected and the transaction hangs and takes a long time to complete.
If you are in a window with the top navbar visible (the part with your name and setting etc.), then you will see a red cross appear with the time running. Clicking the cross will cancel your transaction. But what if you’ve opened up the main window in a new tab without the navbar?