For those who don't know, KaiOS is a closed-source proprietary fork of Mozilla's abandoned FirefoxOS for mobile devices. It's become extremely popular for low-end feature phones in the developing world.
How can it be closed source? What licence was FirefoxOS originally released as? Or you mean that they added new bits to it and kept them closed source? In that case, what's their rationale?
> As such, it allows re-licensing. MPL software can thus be converted into a copyleft license such as the GPL, or to a proprietary license (example:KaiOS).