(2019). The report was released mid-2019 covering 2017 and 2018, based on the title and second page date stamp. This year’s report, assuming one is released, would be posted without any (20xx) at all, even if it covers 2019.
I would have corrected the title for this post as:
State of Mozilla 2018: Annual Report (2019)
Which is a bit hilarious, but complies perfectly with the guidelines!