+++ This bug was initially created as a clone of Bug #119977 +++

Bug 119977 has just implemented an awesome feature of allowing a single mailing list to be expanded via context menu.

We should improve the UX for multiple mailing lists which are part of the selection.

• Whenever at least one mailing list is part of the selected pills, show the Expand List command in the context menu, regardless if a mailing list has focus or not.
• When multiple mailing lists are found in selected pills, change label to Expand Lists, and expand all of them when the command is executed. This will make scenarios of expanding multiple mailing lists much more efficient and convenient, also for enterprise users.

The current behaviour is wrong as we enable the Expand List command when there are multiple mailing list pills in the selection and one of them has focus, but it will only act on the focused mailing list and ignore the other selected mailing lists. That's a ux-mode-error...

The came up in the early version of the patch, it was decided to only do the target pill:
https://phabricator.services.mozilla.com/D116052?id=446458#3781868

Indeed, it's a context menu for a specific pill. Let's not over complicate it.