Well, when you consider that every bug fix carries with it the chance of introducing a worse bug, sometimes holding off on a non-critical fix until everybody's back from the holidays and able to work 100% again doesn't seem like a bad idea.

Having some % of FF 43 users (who're about 3.5% of the browser market according to netmarketshare.com) experience degraded but functional video may be better than, say, a 1% risk of breaking youtube for 100% of users and not being able to fix it for a day.