Grandmaster LxCenter Core Team Member LxCenter Representative
Mostly likely the case is that a firewall is simply blocking the access completely. From that browser command prompt, you can run iptables -L to list the rules. iptables -F would flush the rules, but not save it. The way to save the rules depends on your distribution.
From a browser, it isn't using your workstation to connect. It is providing you a window to send a command and PHP processes that and uses a shell function to execute it and returns you the result. I doubt you are using SSH in this case. Now if you are using SSH, the PHP script could add allow your IP address by adding a rule to iptables and then remove you, but I highly doubt this.