Council of Elrond

Fireworks can be played during MH.

Assuming I move from a tapped site to another tapped site on the board.

In MH I am considered to be en-route so I am present at neither site. So which site gets untapped?

The 'known' site of origin or the new site (though I could actually still be send back/diverted etc.)

Ritual. Playable on an untapped sage at a tapped Border-hold [ ] or Free-hold [ ]. Tap sage. Make a roll and add the mind of the sage (+10 if a Wizard)—if the result is greater than 12, the site untaps. The next time the sage would otherwise become untapped make him tapped instead and discard this card.

Underline mine.

So Fireworks may be played during M/H phase but not on a sage that is not at / site.