Seems like a nice feature. I just enabled it and there's some overlap with ublock origin.

That is, when I load some pages with tracking protection and ublock, the number of requests blocked by ublock is smaller (but still far from 0).

After looking at Firefox log, it doesn't seem this feature blocks anything that was not blocked by ublock. But this might be wrong, I only tested a few sites, and I have no idea about the internals of these tools.

More knowledgeable info would be appreciated.