Cannot change settings on certain popups due to missing browserAction button

[T-vK]

Browser: Firefox 58
Extensions: uMatrix, uBlock, FoxyProxy (but not active)

Certain popups don't display browserAction buttons. Thus it is not possible to apply any settings on them through the UI.

How to reproduce:
For example when you buy something on ebay.de, you won't be able to pay for it with PayPal because the PayPal popup that ebay spawns doesn't have any browserAction buttons.

Ideas:
Consider using pageActions instead or in addition.

[gorhill]

See "How to access the popup panel when there is no toolbar".