Especially on Android, where Chrome doesn't have uBlock or extensions, and Firefox does.

Not to mention the million hooks Google's apps put into Chrome search, browsing history, etc. If you use the Google Search launcher to open an app, it sends which app and the time it was opened to Google!

I'm disappointed that the death of Firefox OS and Ubuntu phone leaves us with little choice for FOSS smartphones.

Android is not FOSS. The Android Open Source Project (AOSP) is, but that excludes all the closed Google apps upon which more and more Android apps rely on. Almost every smartphone ships with Android, not AOSP, therefor there really isn't a FOSS smartphone market.

I use Chrome / Chromium with uBlock Origin, and am basically ad free. uBlock Origin works great on Firefox too, and I'm a Firefox user on Android solely because this extension exists, and Chrome for Android refuses to run extensions.

Heck, even Microsoft Edge can run ad blockers now. There's no shortage of options if ads are the primary thing keeping you away from competitors.

Not sure what you're referring to, I see the same amount of ads regardless of which browser is used... Have you tried using an ad-block extension?

Ad-infested?