Reddit announced the cause of the outage.
https://www.reddit.com/r/help/comments/s4095g/resolved_block...
> PetGorignac, Admin, 2 hr. ago
> Hi folks,
> I was the incident commander for this one and came by to drop a bit of information about what happened here.
> We were attempting to mitigate some problematic traffic that had been causing a low amount of site errors over the past few hours. In doing so, we identified some traffic characteristics that we believed correlated with the error rate and attempted to block it. It turns out this blocked Firefox traffic, which we noticed relatively quickly, leading us to revert the change.
> Apologies for the disruption!
> (Also kudos to the commentor who had a great RCA, but sadly the comment got deleted before I could respond)