I must be weird, but that was an actually useful feature, imaginative and with no parity elsewhere. For some period of time I used Firefox solely because I enjoyed that feature.
I still check in occasionally hoping to see it when I have to troubleshoot a related issue. And when I bring it up to people who remember it…well they seem kinda bummed about it being gone as well.
To be sure, its not a ravenous need, but it was a nice to have, that caught certain issues way early on. Even none of the 3rd party versions work anymore…
Tilt uses some super powers that I believe are unavailable to WebExtensions, which is to copy over the contents of the DOM to a canvas. It was also architected to be single-process, so it would require a lot of migration to make it multi-process.
The z-index tool would be much easier to port, and is based on stacking contexts, which I found really useful to understand my stacking order.