Described herein are salts (e.g., fumarate salts) of 3-(2,5-difluorophenyl)-7-[1,1-di(methyl-d 3 )ethyl-2,2,2-d 3 ]-6-[(1-methyl-1H-1,2,4-triazol-5-yl)methoxy]-1,2,4-triazolo[4,3-b]
pyridazine and particles comprising 3-(2,5-difluorophenyl)-7-[1,1-di(methyl-d 3 )ethyl-2,2,2-d 3 ]-6-[(1-methyl-1H-1,2,4-triazol-5-yl)methoxy]-1,2,4-triazolo[4,3-b]
pyridazine or a salt thereof, and uses thereof.