If you run Firefox from its default mechanism, it will update itself and ask to restart before applying the update, and will continue working forever, never updating until you restart it.

I'm on Firefox beta for a year or so and never seen this - it politely shows update notice and that's all. Updates itself once I close all open windows of FF. Wonder why Nighly do different things here. From another side - running nightly is expected to be not the same smooth as stable release.

Discord is a great example, because it's very far from being optimal in so many regards. It could be written in C++ and be so much faster, use so much less memory, it could be more reliable in many aspects… But because most people don't care, what Discord creators do is roughly the most meta-efficient (money efficient?) thing to do.