Originally Posted by mozilla

It sounds like an MTU issue. Extremely simplified: internet "packets" are limited in size (the Maximum Transmission Unit), and when something along the way - like a Wi-Fi management system - adds overhead to the packets, fewer data can be transmitted in the unit.

Normally there are systems in place to detect and coordinate how much data can be transmitted, but when this breaks, for example, due to a poorly configured firewall, connectivity issues will occur. Typical MTU issue symptoms are some websites that are working normally, others don't work at all, and some websites only load partially before they time-out. How many websites are affected depends on the gravity of the MTU issue.

It may have been temporary, but definitely something to keep an eye on.