Very useful!

Currently suffers from a couple of bugs. It uses the same shortcut (CMD/CTRL-7) as switching to the seventh tab; it will thus do both. To use the extension, you need to call it from a window with less than 7 tabs, or to have your content on this tab already. Also, calling the shortcut more than once will show the UI again on top of the existing view.

Simple and does the job. I was using HeadingsMap before webextensions and I missed that, so thank you!