This extension accomplishes the basic task of showing two pages side-by-side. But you have no real control over which tabs get split (it's always the current tab plus the next tab), you cannot easily switch which tab is shown in the tile after you launch the tiled view, and worst of all if you have multiple monitors, there is no way to control which monitor the split view pops up on (it's always the primary monitor even if Firefox is on the secondary monitor).