Hi   !
Find the add-on in   about:addons  (not   in   'about:debuging')   and click the debug button on that page.
See:   https://developer.mozilla.org/en-US/Add-ons/Add-on_Debugger

https://developer.mozilla.org/en-US/docs/Tools/about:debugging

The about:debugging page provides a single place from which you can attach the Firefox Developer Tools to a number of debugging targets. At the moment it supports two main sorts of targets: restartless add-ons and workers.

the-edmeister said

https://developer.mozilla.org/en-US/docs/Tools/about:debugging The about:debugging page provides a single place from which you can attach the Firefox Developer Tools to a number of debugging targets. At the moment it supports two main sorts of targets: restartless add-ons and workers.

Hi, the-edmeister. The extension in question is not a restartless add-on, and not a worker. It is a xul add-on. If about:debugging does not allow to debug that kind of addons, is there any other way?

Happy112 said

Hi   !
Find the add-on in   about:addons  (not   in   'about:debuging')   and click the debug button on that page.
See:   https://developer.mozilla.org/en-US/Add-ons/Add-on_Debugger

Ho Happy112,

I do not have a debug button for either of my addons on the about:addons page. Only a "Debug Add-ons" in the dropdown menu, that leads to about:debugging. However, at the page you provided, I found

The Add-on Debugger is not available for restart-required XUL overlay add-ons. To debug add-ons like that, use the Browser Toolbox instead.

https://developer.mozilla.org/en-US/docs/Tools/Browser_Toolbox

I will try that.

In fact, Browser Toolbox solved my problem: I can debug my extension using Browser Toolbox.