Maybe I (or someone) inspired by custom browser project like the OPs, will someday bundle FF with crucial add-ons for iOS and ship that through Github. It would probably need a dev account to install it in iOS/iPadOS, but it sure would be worth it. What I don't know is if regular FF add-ons (uBlock, cookie autodelete, etc.) will work on iOS FF since it runs with a bundled Safari webkit renderer, another Apple iPhone v1 2008-era-restriction for such delicate piece of hardware (weak battery, mem and cpu) that makes no sense now with powerful 2020 devices.