I like theming , I am already a Firefox user. I think the sad reality is that for more adoptions , in the order of numbers that chrome puts up , Firefox needs to be a default application ; the common users doesn’t want to customize anything ( my hot take ).

I don’t think it is important that Firefox gets to those numbers as long as they can generate enough revenue to keep going.

https://libro.fm/ you can buy audiobooks through independent book store and they are drm free. It’s great. If you want more of an eye patch solution. You could rip audio from YouTube. There tends to be a lot of books uploaded there.