As Pure_BY already mentioned in Pure_BY's reply to Plus!'s & WLM's keyboard shortcuts
Use a tabbed web browser? Even if you don't, you might find tabbed conversations useful for organizing your chats by converting a myriad of windows into a simple single one. Vertical tabs on the left, normal tabs on the top. You name it. You can also use tabs to group just some special chats and keep all the rest in normal windows if you want.
But this last aspect never was a feature of Messenger Plus! Live, as it had been removed since Messenger Plus! Live 4.00.234 was first released in June 2006, thus it should be removed from the Features page aswell, as it hasn't returned in 4.50 either.
Originally posted by changelog for 4.00.234
Tabbed Chats. The feature has been redesigned to be more "user friendly", however, this required some previous options to be removed: the possibility to group/ungroup chats manually with a key combination has been taken out. No more auto-switching to a chat with unread messages either. Emoticons are now displayed in the contact's names and the tabbed bar integrates better in the window.
I just noticed that this issue has been brought up several times in the past, but hasn't been fixed since.
Something wrong in the features page
Tabbing some special chats-Is it possible, it is written on website
Plus!'s & WLM's keyboard shortcuts
But as far as I know, no thread has been posted in the correct forum for this yet, which is Forum & Website, so here it is.