Haven't actually looked at this early adaption of what "fox splitter" does today - just adding this comment for later bycomers to find this term to look for!
This has great potential but needs work. Each time it's used it opens a separate tab with a split window defaulting to the developers site. The same happens when switching from horizontal to vertical mode, loosing the site(s) I placed and defaulting again to the developers site(s) (One english, one native language version). Very aggravating having to replace site urls and reload the split tab each time.
I've wanted a feature like this in windows for a long time that's like the split window features in the Konqueror browser found in many Linux OS's. As stated, this has great potential, and I look forward to improvements with anticipation. Please keep working on this one Visuddhi. Great extension! With some refinement this could 'hopefully' become an integrated feature of Fx.