After Firefox 4 upgrade - Twitter login does nothing (?)

Today I upgraded to Firefox 4. I have been using 1Password 3.5.9 and FireFox 3.x (last release) very happily. I followed instructions. 1Password appears in the FireFox toolbar, and login seem to work correctly for each site I've tried - except for https://twitter.com

I have four twitter logins all rooted at ref url https://twitter.com. When I edit any of the Twitter logins, the 1Password def shows only two fields: username and password.

If choose one of the Twitter logins in FF4 the browser navigates to the Twitter home page with username / password prompt in the upper right, but never logs in or leaves the home screen. If I'm on that page in FF4, the browser pulldown shows all four accounts, but when I choose one, nothing happens.

The same login works like a charm using the 1Password browser button in Safari.

I looked through the FF4 FAQ and reinstalled the 1Password FF4 extension following the step by step instructions.

Any clue? I have Firebug, Page Speed, Google Toolbar as the only FF4 Extension installed (other than 1Password). And FF4 / 1Password seems perfectly happy with the six or so sites I've tried other than Twitter. I cleared FF4 cache, no change.

update: ONE of the four saved Twitter logins seems to work with FF4. It uses different field names.

changing the field names (manually) of other saved logins from username to session[username_or_email] and password to session[password]

seems to work - but would like to know if this will be a bother and manual action for many other sites (I have a lot saved). If I run into this again, deleting the login and letting 1Password prompt for a new saved login might be ok. But then I need to be careful to save the high-strenght password for that site.
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