The instructions are baffling, and need to be rewritten more simply. But the addon does the main thing I want. It provides a list of all the tabs in all the browser windows.

Let me save you some time. Go to:
Tools menu > Addons > Extensions > All Tabs Helper > Options > Appearance section.

There you can increase the "BrowserAction popup width" with the arrow to a maximum of 600 pixels. This is the width of the popup list that shows up when clicking the addon icon. This makes the list wider and more easily scannable. If you click in the form, you can type in an even larger width up to 800 pixels before the list width maxes out on my monitors: 2560x1440 and 1920x1080.

In the "Multi-window" section check the box for "Enable multi-window mode".
Also, in that section check the box for "List host windows tab first".

Those 2 changes put all tabs from all browser windows in the list. It puts the tabs from the current window at the top.