One more data point that is useful for narrowing it, and one thing to rule out.
When this comes up, the same symptom shows up on Windows, macOS and several Linux distributions at once, on the same browser version. That is worth treating as evidence rather than noise: something identical across all three is not a packaging problem, so the usual platform-specific advice — reinstall the package, try the other package format, clear the profile directory — is a dead end. Do not spend an evening there.
The thing to rule out is the site rather than either program. A fair number of login pages have moved to asking for the username first and rendering the password field only after you submit it. If the menu used to appear because both fields were present on load, it genuinely will not appear the same way on a two-step form, and the change was the site's. Test on two or three unrelated logins before concluding anything — including one you have not visited in months, since that removes any saved-state explanation as well.