Exceptionally slow or sluggish; not fast at all. (The addition of "January," which is among the coldest months in the Northern Hemisphere, serves to intensify the meaning, as molasses is especially viscous in the cold.) This old laptop my dad gave me takes forever booting up, and then it's as slow as molasses in January the whole time I use it! Come on, Becky, you're slow as molasses in January back there! Pick up the pace and keep up with the group.