Rated 2 out of 5 stars
"1) I think that each "pane" should have navigation toolbar."
I couldn't think of anything more stupid if like most users you just want to view another tab page alongside an existing one. Which is what most do. And its much better to utilize the same navigation ui based on which panel is actually active or last active. So only the extra stuff is splitting the tab toolbar so users can have seperate tabs that display on its corresponding panel below. Sure its really only going to be good for dualscreen though.
The addon would be better if could actually implement this better functionality:
http://img833.imageshack.us/img833/4386/dualview.jpg (a proper secondary tab bar! for the 2nd panel split)
screenshot explains all. Splitting more than twice is almost never done, though its a nice added novelty, but the actual workflow and tab logic on it is completely illogical and could be improved. Try Maxthon 2/3 for a better tab splitting demonstration.