[sharps1]

They originally started with Gecko and switched to Chromium.

"There were a ton of issues using Gecko, starting with (at the time) no CDM (HTML5 DRM module) so no HD video content from the major studios, Netflix, Amazon, etc. -- Firefox had an Adobe deal but it was not transferable or transferred to any other browser that used Gecko -- and running the gamut of paper-cuts to major web incompatibilities especially on mobile, vs. WebKit-lineage engines such as Chromium/Blink."

https://news.ycombinator.com/item?id=28941623

[dabockster]

And nowadays, I'd argue that there's more human eyeballs watching the Chromium source code vs the Firefox code.