#i tried looking into lace for funeral customs but couldn't find anything

[eccentricmya]

I think, after Fëanor's fiery death, the Fëanorians burned their dead. Which went against the custom of burying the dead among the Eldar.

Burial was seen as the acceptable method of returning the hröa to Eru, to be reworked into the Song. But burning was frowned upon as it disintegrated the body Ilúvatar had given. It was considered a deliberate destruction of His creation.

So Fëanor's act of self-combustion and his followers' insistence on well, following in his steps was yet another act of defiance on their part.