There is this addon(aka extension) for Firefox called "Tree Style Tab" (Show tabs like a tree.) by YUKI "Piro" Hiroshi, which is just perfect for Firefox. Now, I've noticed that while I'm trying to do some goal, along the way something else pops up which needs to be resolved first before I can continue to toward goal, so I'd like to branch off from the current point, in the pursue of resolving it and once I'm done, I'd be right back to where I was. Also, this can happen to an arbitrary depth, not just 1 deep. Window Buttons in treestyle would make it easier to see which buttons are part of the branching, when wanting select any to focus. Treestyle Window Buttons would help with this, if it were implemented(if it even can be possible, unsure), it would work similarly to "Tree Style Tab" extension. Well, maybe there needs to be a way for it to know when to create a child tab, for example if current focused app is xfce4-terminal and I want to start another via a shortcut like ctrl+alt+d, how would Window Buttons know it should be a child or a sibbling, in the list of Window Buttons ? Not sure yet. Also, this implies that the Window Buttons plugin(?) or Item(what's it called?), would be added to a panel that's in Deskbar mode(ie. tabs would be vertically stacked), or else it wouldn't work if horizontal.
I think this type of feature is impossible to implement without a window manager that supports this kind of "stacking". And finally, the window buttons plugin relies on libwnck which surely doesn't provide anything to enable such a feature... So the realistic response is: it's not feasible.
Right, thanks.