How to extend the developer tools with an extra tool

Developer Tools
#1

I didn’t develop a firefox addon yet, but I’d like to tinker with it by adding a new extra tool (like the ruler or the screenshot button) to the developer tools.

Is there any documentation about this somewhere so I get a clue how to start?

Thanks a lot! :slight_smile:

#2

https://developer.mozilla.org/en-US/Add-ons/WebExtensions/manifest.json/devtools_page only, seems no APIs for adding button to devtools in Chrome & Firefox.