I really like Firefox on my desktop PC and it is much faster for me since the Quantum update.
I like Firefox for Android on my phone and tablet, but find it quite slow to render pages compared to other browsers like Brave or Chrome, even though it is the most configurable. I hope that the speed will improve over time to match desktop. For this reason, Brave Browser is currently my primary browser on Android. Brave does not support extensions but has a lot of extras built-in (like ad blocking) and is fast. You might also want to look at Firefox Focus.
My favourite ad blocker is Adguard AdBlocker but I also like uBlock Origin.