I'm using Tile Tabs WE now instead of Tile Tabs, since that no longer works. Tile Tabs WE does it's tiling by opening new windows as a workaround, but I feel like that kind of misses the point.
According to the dev, a version that would work more or less like the original is waiting on https://bugzilla.mozilla.org/show_bug.cgi?id=1318532 which apparently has implementation but has been cockblocked for 3+ months by somebody in the review chain.
Ironically more Servo features could actually make this work better than the XUL version, such as supporting GL/CSS 3 transforms on the <webbrowser> components.
Take a look at Servo's current UI for how this could work.
Of course this doesn't help much with Quantum in its current state.
Does anyone know of any alternative?
https://addons.mozilla.org/en-US/firefox/addon/tile-tabs-we/