Here's what I believe happened, and someone less lazy than I may wish to file a bug report:

The 83.0 notes say that on OSX, minimized windows will no longer suck as much juice. In past versions, once you entered your master password, any minimized windows with a realm/password-challenge would maximize, and expect you to hit OK. In this instance, I had a minimized window with a URL in a realm, and on launch, it was not popping up to ask for my OK. Since this one realm had not been cleared, subsequent requests for other realms were waiting for the first credential challenge to be OKd, but I wasn't even aware this was waiting to happen. A solution would be to go back to the old behavior. Another would be to approve realms with the default values (hit "submit" for the user, basically), and only pull failures forward. Another would be to let these challenges be dealt with in parallel, rather than serially. A fourth solution would be to simply notify users of the need to deal with this manually.