Firefox OS returned as a KaiOS, which is now powering many feature phones, among which the Nokia 8110 4G, 800 Tough, and 2720 Flip. KaiOS is a bit smarter feature phone since it supports many Google applications, but the OS is still not performing very well. The reason for that lies in the older version of the Gecko rendering engine, which is powering the whole KaiOS. Back in 2018, Mozilla Firefox released the Quantum update, which made the Gecko twice as fast, and Gecko got supported for modern technologies. KaiOS was left out of that new Firefox support, but just recently KaiOS team signed a deal with Mozilla, which is going to support the future KaiOS updates like KaiOS 3.0. This version of the OS should be coming on devices in early 2021. Anyway, Techaltar did a great video about this topic, where he nicely explained all that he exclusively found out about the new KaiOS and Mozilla deal. Definitely worth watching!
I am not sure if the new updates will be coming to existing Nokia phones since it is too early to say, but this deal is going to be a much-needed boost for KaiOS that could make Nokia phones that are running this OS more usable.