STR (1) In b2g, load homescreen. Swipe to the left to get into everything.me. (2) Choose "Games" section, then the "Tetris" game. (3) Let some pieces fall and/or move them around. You can see "ghosting" artifacts where the pixels painted for an animated piece at frame i aren't repainted at frame i+1. From what I can tell with paint flashing, the pieces are HTML elements that are moved around, likely transformed. dlbi fixes this.
Possibly duplicate of bug 794686, does this happen on aurora?