Unusable in dark theme (official firefox ones), since text color matches so much with background color. Should have default theme sets for this extension, or even better, allow user configuration for colors of elements or css customization.

Love it!
I'm a user of Headings Map extension which is not compatible with Firefox anymore and I was looking to fill this void.
I would recommend to add 2 features:
* allow to copy anchor link (e.g. link to the id attribute if present)
* add shortcut to toggle visibility

Having an outline of long documents like specifications or manuals is certainly very useful. It is also a valuable tool to a web developer to see your heading structure.

It doesn't support the html5 section algorithm (yet?!), but the dev is very helpful, responds fast and seems to be interested in improving the extension further.