Sources This add-on was built based on the following sources:

Button enabling only on http(s) url tabs:

https://github.com/mdn/webextensions-examples/blob/master/apply-css/background.js

Contextual identities handling:

https://github.com/mdn/webextensions-examples/blob/master/contextual-identities/context.js

Pop-up html/css:

https://github.com/mdn/webextensions-examples/blob/master/contextual-identities/context.html (html) https://github.com/mdn/webextensions-examples/blob/master/contextual-identities/context.css (css)

Icon:

omni.ja\chrome\browser\content\browser\