217.115.41.218 (that's one away from the IP of your first hop) are being blocked by my firewall due to malicious http attempts. Not sure if that's you or not. 

Can you open your browser on http://minip.no and send me your IP address?

Just want to check they are have not been blocked by my firewall. Some IP's are doing non-standard http requests and are being blocked by my firewall.

This is very strange. I'm using UptimeRobot to monitor site uptime from external locations. It's checking tellmon.net from two different locations every 5 minutes. And it's not reporting any downtime.

The pings are only reaching my firewall and not the server. As it should be. Since you can ping the IP, but not access tellmon.net (note you'll need to use the domain name and not the IP when trying to access the site) I'm not sure what the problem is. As other users can access the site just fine I'm having trouble figuring out why the firewall should block only you.

I can see 81.191.167.157 in my logs, but I find no mention of 158.39.96.23 in any logs. I'm sorry, but I don't know what else to look for. http://tellmon.net is available from all the locations I can try from. If the 158.39.96.23 location is connecting via a proxy, make sure it is configured to send the HOST header in the http requests. 

As a side-note I have installed a new firewall today that should take the load much better than the old one. 

Can you attach the tracert log? You should end up at 79.161.150.134.
I'm using UptimeRobot to monitor uptime from two different physical locations. Tellmon.net is responding from both of these.

Does seeing old "sensors" under sensor settings really bother you that much? I figure this to be a small nuisance, am I wrong? 

The "timestamp data" is now just a list of the last "X" events logged. I'll look into it.