36ebff8616
This allows to use the feature from the context menu and is very straight-forward. This has the benefit of working with fission (as print from the focused frame) and so on. Making a checkbox on the UI on top of this is doable, but it is a lot more complex (requires a bunch of both front-end and platform work) because undoing this implies restoring the DOM which "print selection" removes. I think the context menu entry is very useful regardless of whether we add a checkbox to undo it, and other browsers (with smaller context menus) seem to agree. Differential Revision: https://phabricator.services.mozilla.com/D92205
