The loop in HashBytes currently hashes both a word of data (as intended) and the length of that word of data (a constant). This was [acknowledged as a bug](https://bugzilla.mozilla.org/show_bug.cgi?id=729940#c49) when first written, but slipped through the cracks and was never fixed. Differential Revision: https://phabricator.services.mozilla.com/D119466