It looks like 01010101 has unpublished that GifAnimation repository – links are now dead.
Untested, but the original GifAnimation for Processing 1 & 2 does have a “3.0” branch which was last updated 3 years ago.
The README lists Jerome Saint-Claire as the porter – I’m pretty sure that is 01010101, so it looks like maybe the port was migrated back to a branch of the main repo.
Is that working for people on Processing 3?