The first browser extension I ever installed was the original Adblock for Firebird (maybe even Phoenix, I don't recall exact timing), and to this day an ad blocker is the first extension I install on a new browser profile. These days my preference is uBlock Origin but it's still the most important part of an acceptable browsing experience.

Every time I browse the web on my phone it's just a nightmare of nonsense.

Tampermonkey is an on and off thing for me, sometimes I have it installed and use it every day, other times I go years between needing it.