Firefox does offer uBlock, at least, which is a massive relief. I also run (on the router) a large, and after significant modularisation by me, flexible dnsmasq blocklist that addresses another large set of issues.

On desktop (Linux, MacOS), I have and use: NoScript, uBlock, uMatrix, and Stylish, as well as Reader Mode.

It's still often less aggrevating to grab source or rendered text and create a standalone Markdown text, for various reasons.

I'm looking into the notion of a browsing mode that presumes the website designer is an idiot and that the HTML markup is at best a hint at what the semantic structure ought to be -- see concepts such as POSH (Plain Old Structural HTML), and ... a few other things. Work in (very slow) progress.