I have been using Zen-Browser as my main desktop browser for around almost a year (I think). Initially just wanted to give it a try because it has nice vertical tabs that aren't clunky or just an extension. It also looks better (imo) than most of the other FF-forks that I have tried.

On Android I use FF since it isn't Chrome/Chromium and most importantly can turn on basically "Dev Mode" in a similar way that you enable Dev Mode in Android. This allows you to install all normal extensions that you can on desktop FF. Even if that wasn't an option, uBO is installable (unlike basically every Chromium-based option). Really really helps going to websites while on my phone or tablets not feel like a complete downgrade compared to just turning my desktop on.

There are some Chromium and FF forks for Android that do allow some extensions, just not a lot to pick from. And I don't want to use Chromium stuff since it further pushes sites to pull an IE and code sites to work only for Chrome/Chromium.