Do you use a device with open source Android firmware? What device, which distro and what do you do with it? I have a Samsung tablet with LineageOS and apps from F-Droid. Other than displaying dire warnings about the unlocked bootloader every time it cold boots, It’s great for a “recliner system”: email, Web browsing, E-book reader and MP3 player. What do you have, what do you use it for, and how well does it work for you?
Android isn’t firmware. It’s OS. Firmware is embedded on things like the camera, wifi chip, etc. I don’t know of any that have FOSS firmware. I hope I’m wrong.