The new version of Firefox no longer allows extensions to create toolbars so that is no longer possible and not something that I control. Older versions of the extension are available here, but note that they are not supported and will not work in future versions of Firefox:

https://cup.aihedy.com/en-US/firefox/addon/web-developer/versions/

UPDATE: Firefox also doesn't let me create a number of separate icons unless I do so as separate extensions so that is also not an option for me.