Mostly if you find an attached GitHub repository to the software, you can have a bit more trust in it than otherwise, it means that the developer is putting their cards on the table and not trying to hide something nefarious. Of course there are caveats to this but it's a good start.

Running any software is inherently unsafe. It's basically the computer equivalent of eating something given to by a stranger, and you just have to trust them that it's good for you.

But we do it anyway, simply because we have to - not all of us are software devs with unlimited time on our hands.

It basically comes down to whether you trust the origin or not, as well as check the reviews/comments to gauge the reception of other users. If something fishy is going on, word spreads relatively fast.

Tip: While no means foolproof, if the software in question has a github repo, it adds a layer of trust, because that means anyone can review the source.

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).

If you have some sort of decent antivirus/antimalware like Malwarebytes, that would work for standalone applications to an extent.

Browser extensions are a lot harder to check.

Always make sure you get the RIGHT extension from the PROPER SOURCE. Same with most downloads and app store stuff on your mobile devices, but at least with executables, you can additionally run virus scans for some peace of mind.

Some tips...

• Always make sure you're accessing the extension's download/install page from a trusted source.
• Check reviews AND READ THEM. Make sure they don't look suspicious/bot-generated.
• Consider what permissions you're giving the extension. Your browser has a lot of personal and sensitive information... including the "keys" to a lot of your accounts. Basically any website that you don't need to sign into every time you access it? That "key" is stored in your browser.

I believe you can generally trust what permissions an extension or app needs (since the browser/device knows which permission an extension/app uses, and locks them away otherwise), but be wary of the implications of some of them (such as data from other websites, or accessibility features).

As a techie, I can say that's a hot research area. There isn't much useful stuff in it.

Is there a site that transparently evaluates software and publishes its findings?

Well, you just found the Mozilla one. It has told you their findings.

Not much you can do other than researching the current consensus. And for the latter you can try to search discussions about its safety. Good query to start with is "is programname malware/spyware".

Try virustotal.com. You can scan files and URLs.

Both practically and theoretically, it might be impossible. It basically comes down to trusting trust. https://www.youtube.com/watch?v=SJ7lOus1FzQ

As a techie, I would say rather stay away from browser extensions. A lot of them do add great functionality but browser extensions are much more difficult to verify and it's a lot easier for them to be malicious without you knowing