While the splitting-into-separate-windows issue is not ideal, I recognize that it's a limitation of the new Firefox rather than this add-on. Aside from that, this add-on is awesome. I wanted something that was close to Vivaldi's tab-tiling feature. This works great for that and I'd argue even better executed.

Edit for the Developer: Any plan on making Tile Tabs work with the upcoming multiple tab selection feature? Like selecting specific tabs, then right clicking on one to get a "Tile Selected Tabs" option in the context menu?