Twit Side works really well. A few more customization options and the option to add a column based on a search would be nice, but not necessary.

The add-on is beautiful and fits the screen very well. Here, however, it does not display any image, neither of the profiles nor the images of the timeline. :-(

複数アカウントでの利用においてとにかく便利
サイドバーで作業やWebサーフィン中の"ながら見"が出来るtwitterクライアント
これが無いとtwitterが不便で不便で……