Now since your desktop is also behind a firewall you won't be able to ssh or rdp into it from the outside (since they propably won't setup the nat for you)...
what you can try is using a free vpn service like LogMeIn-hamachi
This service is free and works in a way that both your desktop and laptop would connect to a logmein server and the server would then link you up.
This way you can connect to your desktop by entering the ip that logmein gave to you.
Now what you want to do to get connected to it might require you to also run ubuntu on your laptop since I don't know if mac supports this.
You need to setup an ssh server on your desktop by installing openssh-server
In console: [aptitude install openssh-server]
Then on your laptop you can connect to your desktop's ssh server and use it as a proxy...
In console: [ssh -D 8080 logmeinip] (replace logmeinip with the ip that your desktop has on logmein)
Then you need to set your browser proxy to localhost or 127.0.0.1 on port 8080 (also do this for local ip's)
Ans now you should be able to browse the database without limitation.