"Current"? Embedding Gecko has always been an exercise in futility, which is why everyone and their dog adopted WebKit with gusto. Simply speaking, Mozilla always expected people to build on Gecko, rather than with it. You were expected to go XUL and treat Mozilla as your main runtime, developing the whole program with JS on top of it. Embeddability was always an afterthought. They took this approach to extreme levels with FFOS.
Khtml/Webkit used the opposite model and won big.
Funny enough though, Mozilla's insistence on JS as general-purpose was likely a factor in the long-term survival of what was, back in the days, a wobbly and improvised browser-only scripting language. In many ways, you could not have had Node without the XUL years; but the JS explosion happened on Webkit components, (fatally ?) wounding the Mozilla platform. History is funny like that.
This really isn't an accurate representation of what happened. WebKit's success didn't happen overnight, and people weren't jumping on it from the get-go. In fact, there was a long period of people using Gecko and engineering their own embedding/browser solutions because it was widely, and correctly realised that Gecko was a more mature and featureful engine. This was my job for several years before I was employed by Mozilla (and indeed, I did do some WebKit work at the time too - but there was far less demand for it).
It was only through a long period of neglecting these users that WebKit was allowed to mature and become successful. There was a good reason for doing this (see yoric's blog post, linked in my other comment above), but I think we've past the time now where we need to reconsider this direction somewhat.
It didn't happen overnight because any embedding project takes time; but the webkit community expanded relatively quickly as Mozilla simply did not care about their (overall small and shrinking) own share of the market. You said it yourself, they just did not care enough. Look at Qt, which had struggled for a while with producing reliable Gecko bindings and then really turned a corner with Webkit.
Camino was my favorite browser back in the days of PPC macs, I have really missed having a Gecko-based browser with a native interface on any platform since then. Ditto when Epiphany made the switch from Gecko to WebKit for the same reasons (and webkit-gtk is really awful compared to Gecko, every time I try to use GNOME Web these days I switch back to Firefox almost immediately because it doesn't load half of the web apps I use).
Khtml/Webkit used the opposite model and won big.
Funny enough though, Mozilla's insistence on JS as general-purpose was likely a factor in the long-term survival of what was, back in the days, a wobbly and improvised browser-only scripting language. In many ways, you could not have had Node without the XUL years; but the JS explosion happened on Webkit components, (fatally ?) wounding the Mozilla platform. History is funny like that.