[ie8] screen height too small on id-mismatch screen; hides buttons.

[jrgm]

STR:

1. Sign in with account-A@yahoo.com
2. Try to add account-B@yahoo.com to that account

On IE8, the screen is resized for the 'Accounts dont match' screen such that the actual buttons are not visible.

Changing the screen height reveals the buttons:

[jaredhirsch]

possibly related discussion: https://github.com/mozilla/browserid-bigtent/pull/241