The Proton VPN has worked flawlessly, however it should be pointed out that I have had a number of issues based around cloud based services either responding with a 403 or 500. These seem to relate to specific services which detect and deal with proxy related services with a service specific response. When disconnecting from the VPN the servers respond in an expected way.
I believe that this is VPN based and not Proton based. It seems some of those submitting reviews may have experienced this.

Great product but does need some work on its proxy handling ie when visiting a site with stock prices, the price changed and after I refreshed the price had not changed on the display. When I changed end point and refreshed then the site showed the correct new price.

It's sometimes annoying, slow and unstable. But I can't say a bad word about it because it's free and only sometimes bad

This is an easy-to-set-up VPN to use, with a well-known privacy-oriented company, and it's fast, i.e. the speed drop is not at all noticeable even with the free (non-media) bandwidth.

Unfortunately, if the extension is kept running while the computer goes to sleep, etc., the internet connection for the browser becomes unstable, including not being able to connect to any website. Turning off the extension restores the normal connection, but turning the extension back on still causes problems. At this point, removing and reinstalling the extension is required to get it working again. This is non-ideal. Some other reputable VPN providers may be easier to work with than this.

Good extension, but I confirm the bug reported by another user. If I close Firefox (Ubuntu snap) with the VPN connected and shut down my computer, at restart when I launch Firefox there's a notifiation indicating that the VPN is connected but the browser cannot reach any website and the extensions seems broken (blank menu on icon click). The only way to retrieve a working Firefox situation is to unistall the extension (if only disabled, Firefox stops working when reenabled).

Sometimes bugs out and requires a full re-install to work again.
From my limited testing it seems to be related to closing the browser while the vpn is connected.

Servizio molto semplice, comodo e che rispetta la privacy

firefox and linux broken. both versions have authentication persistence issues. log out, disable, re enable, re log is only fix. been like this for ages. why does the linux version suck so bad in comparison of windows....

With only this vpn specifically proton services are not reachable, but work with different vpn.
what a joke !!!

Proton is a really good service, but VPN latence is really bad compared to NordVPN which is one that I tried also!

This add on, is constantly having problems with Firefox, works fine in other browsers like Vivaldi, it was working on Firefox, suddenly when I connect, the addon on Firefox, it begin to give me this message to all sites:
"
Secure Connection Failed

An error occurred during a connection to google.com. Cannot communicate securely with peer: no common encryption algorithm(s).

Error code: SSL_ERROR_NO_CYPHER_OVERLAP

The page you are trying to view cannot be shown because the authenticity of the received data could not be verified.
Please contact the website owners to inform them of this problem."

NOTE: I don't have the Proton VPN client working on windows, just using add on with browser.

I'm using this on linux mint, and basically whenever i install it, it will work for a few hours. Then the next day when i try to load any page, it will fail. Even if I disconnect from the VPN it still fails. The only thing that works is to delete the entire extension and redownload it and log in, which takes too long.
Need to fix this issue, otherwise app unusable

Funciona, y funciona bien.