This addon spies your country, and if they don't like it, it restricts you to a single slow proxy. It does this even if you register it in a different country, just because you used it at least once from that disliked country. Even if you login from the first country ever after.

Also it uses binary WASM module in its code so not even Mozilla probably knows what it does with your data since they can't simply check its full code or functionality.

Not to mention one of the four free proxies was either broken or compromised since it returned SSL errors on random proxy connections.

And finally, registration is mandatory, even for a crippled 15 minute per session free experience, and links your IP to your account so it's trivial to track all your activity.