It's a webkit engine based browser, actually it uses webkitgtk. Now webkit is the engine on which safari (apple) is based as well, and it's been there for some time. blink, which is what chromium based browsers use, is a fork from webkit with its own extras.
So it all depends, chromium based browsers are all blink engine based browsers, which are pretty related to webkit engine based browsers (midori is not the only one BTW). As well as there are a ton of blink based utilities such the electron ones (chromium in disguise), there are still quite a bit based on webkit, specially gtk applications.
gecko as opposed to the other major web engines never had some sort of toolkit that would make it easier for other applications than the mozilla ones to be based on it, and it seems there will never be such toolkit, even less with the dominance of blink based browsers and applications, and in a lesser way but still high use webkit applications and browsers.
If looking for actual alternatives to what dominates the market, I believe gecko is the option at the moment, and if the FF defaults are unsane, I'd strongly suggest using Librewolf, which is essence is FF with much better defaults, it partially uses arkenfox configs, but it's independent and has its own decisions, and also removes very few blobs like pocket at build time.
Eventually servo might become the web engine to look for, and perhaps verso the web browser based on servo. But they are still in early stages as to be considered for day to day regular use. I'm not sure if servo is both a web engine and also offers itself as a toolkit so other applications besides a web browser can be based on it, similar to webkit or blink, but I believe that's not the case, at least not yet, though I wouldn't put my hands on fire for this, :).
Bottom line, you might want to take a look at Librewolf.
Unfortunately divestOS is retiring, and Mull, something like Librewolf but for AOSP based devices, has ceased development. I'm really hoping someone capable of forking it does it...
