Phones that run neither Android nor iOS have been falling behind in terms of their browser and web-based support. Mozilla and KaiOS (the mobile platform most likely to run on such devices) have addressed this through a new partnership by which the former will keep devices running the latter much more up to date in their ability to use the internet.
https://www.notebookcheck.net/Mozilla-and-KaiOS-new-partnership-may-result-in-a-better-future-for-feature-phones.457460.0.html
A shame Mozilla killed its own Firefox OS ! Kai os is just a "bad" copy without interest : we're living in the 21th Century, while feature phones belong to the past. And when you had a touchscreen with Firefox OS, you don't want to go back to a feature phone without !
One day, someone will make a webphone again, because navigators are far more flexible than Java or C++ progamming. But this time, it will running with webkit, sadly for Mozilla...