This might be larger than just the brokerages, as I'm seeing DNS issues across a variety of investor relations pages, too.
Reddit discussion here:
https://old.reddit.com/r/Fidelity/comments/opgjlm/fidelity_is_down/
Reddit discussion here:
https://old.reddit.com/r/Fidelity/comments/opgjlm/fidelity_is_down/