#Mozilla choosing to kill embeddable Gecko (make it a #Firefox only engine, essentially) over a decade ago was such a tragic mistake.
Alternative browsers & desktop apps had no choice but to go with WebKit or Blink/Electron.
As a result, Mozilla have nobody to blame but themselves for their minuscule marketshare and nil developer mindshare today.
Further readings:
* https://lwn.net/Articles/436412/ (circa 2011)
* https://www.chrislord.net/2016/02/24/the-case-for-an-embeddable-gecko/ from @Cwiiis
* https://dutherenverseauborddelatable.wordpress.com/2016/03/07/the-gecko-monoculture/ from @Yoric