[roca]

I don't have any direct insight into why the Atom people chose Chromium but I can see a few reasons that are more likely than "features":

-- Chromium was faster. (For Electron apps you don't really care about Web compat, where Firefox was ahead of Chromium for a while, but you do care about performance.)

-- Chromium was already multiprocess and had some other architectural advantages where Gecko was still catching up. So, less upcoming architectural churn.

-- Chromium had Google's resources committed to it. (Google's shine has worn off a bit since then but it's still a powerful effect.)