Even as a power user… You can’t.

And, in the 21st century, nothing on your computer is safe and private, least of all, browser extensions.

Even if an extension is safe today, with a tiny handful of notable exceptions, it will be”monetized”, or bought and sold to someone that will use it to install adware on your system, train their AI model, or steal your personal information.

There is no feasible defense to this for a layperson, other than absolute transparency in FOSS, and even that is under attack via flaws in the software supply chain.

The best a layperson can hope for is that major vendors care more about exclusivity and locking others out of their ecosystem, such that they are the only ones who have full control of your data (Apple, Google, Microsoft).