The textbox size inside Add template dialog is too small on Firefox. Not sure since when it's broken.
The action fields are using display:table-cell, which means they need a display:table parent. They did when first implemented, but that appears to have been lost during various refactors.
Since only one weird case is affected (ActionFieldLayout with align: 'left' and no label), I would rather work around this in VE (it makes no difference to use align: 'top' instead; I submitted a patch), and figure out what caused this new issue before we make changes (I think nothing relevant changes in our code, we should try to bisect, or it might be a Firefox bug).