I think our focus for now should be bug 1657250. Whenever we can break the opener relationship of a popup,
window.name and all other problems with popups are automatically solved.
I suppose once bug 444222 is fixed we could add a preference that removes the check for the type of top-level browsing context and clears
window.name unconditionally upon a cross-origin navigation, but figuring out how web-compatible that is will still be quite a bit of effort and popups will remain problematic due to their other properties.