I thought Mozilla was more so they are stopping Firefox OS and employees may move to another team?
Is Pandora still alive in 2017?
But why are they hiring at the same time?
they're refocusing what areas to target, so they're laying off + hiring -- some of those people will be asked if they want to move to their new teams else they'll get some severance + job placement help
Once there is more than a single product being produced by an organization, hiring and firing is not generally correlated.