Almost perfect for its purpose. I would ask for the ability to change the color of the icon to match the theme.

Works. Put a very light gray cross icon (the icon is different from the addon icon, and no screenshot is provided), the icon sits next to the URL bar, one click and the current tab is closed.
But for visual reasons, I prefer Close tab context menu, that shows a bigger, dark, black icon.

The icon should be customizable, it would be better, or less difficult to see. This addon is for people who has few icons in the bar, or want a very unobtrusive icon.

@Andralon No screenshot is not good for users, but it's never a reason for a one star review!!!!

For some reason the good folks at Mozilla decided I did not need this extension, so it was disabled.

While I would prefer the ability to tell Mozilla where I want my close tabs button(s), this extension does exactly what it says and it does it well.

As for the ability to resize the icons, you could rename them, but it could possibly end up disabling the extension if the Mozilla tactics are similar to those of Microsoft for verifying drivers, etc.