LobbyTracker

[theMiNsta]

since this is a problem with your config I searched for it on the Steamforums and they had this to say:

[HKEY_CLASSES_ROOT\steam]
@="URL:steam protocol"
"URL Protocol"=""

[HKEY_CLASSES_ROOT\steam\Shell]

[HKEY_CLASSES_ROOT\steam\Shell\Open]

[HKEY_CLASSES_ROOT\steam\Shell\Open\Command]
@="\"C:\\Program Files\\Steam\\Steam.exe\" \"%1\""

Where it says Steam.exe in the last line you probably have the path to iw4mp.exe
just change that, restart Firefox and try again.

The data is the same. It says Steam.exe

Darn it.

But I don't know if I explained my situation properly.

When you go to LobbyTracker - a serverbrowser for MW2 you get the list of servers.
I had clicked the hyperlink on the right, the username, for the first time, and it prompted me which "forgot what it said" program to run it from.
And there is a radio button on the left bottom corner asking if it should remember and keep the preference.

I first tried deleting everything I can from firefox with ctrl+shift+delete
which didn't work..