It is not the same as the old Tile Tabs extension. However, it's the best we have in the new Firefox Web Extensions system.

It does the basic job of showing two tiles side-by-side, and then restoring them to one window when you are done.

Use Ctrl-Shift-UpArrow to jump to a new tiled layout. Use Ctrl-Shift-DownArrow to close the layout and get back to one window.

Good job to the developers for giving us back some of the functionality we lost when Firefox killed the old Tile Tabs extension.