Is it possible to use Safari on OSX with "panes" like vim splits I'd like to have two "tabs" open in one window, but with the content of the two displayed pages simultaneously visible like this:

==================
|  content of 1  |
|  content of 1  |
-------------------
|  content of 2  |
|  content of 2  |
===================


I don't want the toolbar and location bar atop each content area, but I could tolerate this.

The difference between this arrangement and just two Safari windows opened one atop the other is that if I resize the single containing window, the panes resize in lockstep with it.

By the way, it would be even better still if I could have these groups of panes within a tab, and tab between such groups (again, like vi(m) tabs/splits).

This doesn't seem remotely possible with basic Safari, but maybe a plugin enables it?
I am not aware of anything, Safari extension or otherwise that would allow you to split a tab in that way (one over the other, both visible, if I understand correctly). Though I am not the end-all oracle of Safari extensions. Searching Safari extensions repositories (apple or others) would be how I would approach this.

Perhaps there is such an extension for Firefox, Chrome or even Opera that I am not aware of?