When you are using proxies with your Virtual Browser Profiles [link] it can be essential to test if they are working.
With the Proxy Test Tool, you can fast check if everything is fine with the proxy connection without starting the Virtual Browser Profile.
This tool tries to find connections with these sites: Google, Archive.org, and Wikipedia. So, if any of these sites become unavailable, it uses another one.
If the tool can make a connection with any of them through the proxy, then you can be sure that the proxy is working.
There are proxy providers who blacklist websites, or their proxies are only working on a couple of whitelisted websites. Please make sure that the above websites are allowed by your proxy provider.