> What would make you trust a NEW security extension in 2025?

Time. I wouldn't trust it while it's new. I'd develop trust in it over time as I've observed the results of other people using and examining it.

> Would you ever pay for browser security ($3-5/month)?

I don't rent software, so I wouldn't pay a recurring fee. A one-time fee isn't out of the question, though.

> Is Manifest V3's limitations (30k rules, webRequest restrictions) a dealbreaker even for security-focused extensions?

Pretty much, in that I wouldn't be using a browser with that limitation in the first place.