It's not a lot different, in fact, they've just remade our X-Tag components into heavier, less DRY, less modular copies that range from 40-60% larger than their equivalent X-Tag originals, while at the same time managing to reduce browser compat and feature coverage (for ex: Brick Deck lacks the transition support X-Tag's provides, and it's actually larger!)
Compare it for yourself:
Brick Flipbox: https://github.com/mozbrick/brick-flipbox/blob/master/src/br....
vs
X-Tag Flipbox: https://github.com/x-tag/flipbox/blob/master/src/flipbox.js
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Brick Deck: https://github.com/mozbrick/brick-deck/blob/master/src/deck..... AND https://github.com/mozbrick/brick-deck/blob/master/src/card.....
vs
X-Tag Deck: https://github.com/x-tag/deck/blob/master/src/deck.js