Hey Spectre,
Not sure if it will help you but, a friend of mine had the same issue a while back and if your sure that yours is not connectivity / firewall related you could try the same fix that worked for him. This was over a year ago though...

I had him close steam, go into his steam directory and delete the following files (they should auto-update from steam next time you open it, I just tried it on my pc to make sure)
Steam.dll
SteamUI.dll
ClientRegistry.Blob

Deleting those 3 files is kind of a generic "steam is f*cked up" fix...
There were a couple more that I deleted as well if that doesn't do the trick that are in the config folder inside of your steam directory. These will auto update when you connect to a server for the first time.

config\serverbrowser.vdf
config\masterservers.vdf

Not sure if this will help you but it worked for my buddy like a year ago. It will drop your favorites out of your list so write them down or remember them if you have a big server favorites list.

Hope it helps.