Mozilla Firefox 82: In the crossbeam rust crate, the bounded channel incorrectly assumed that Vec::from_iter had allocated capacity that was the same as the number of iterator elements. Vec::from_iter does not actually guarantee that and may allocate extra memory. The destructor of the bounded channel reconstructs Vec from the raw pointer based on the incorrect assumptions - this is unsound and caused a deallocation with the incorrect capacity when Vec::from_iter had allocated different sizes than the number of iterator elements. The impact on Firefox is undetermined, but in another use case, the behavior was causing corruption of jemalloc structures.