This thread refers to this post:
http://tremulous.net/phpBB2/viewtopic.php?p=10643&highlight=#10643Juno: if I understand well what you said you get the firefox pop-up window but neither "open with" nor "save to disk" are enabled... right?
The only thing I can think at is that you have another window opened in background.
I know it's a stupid question but: have you clicked twice on the link? Because if you click twice you'll get 2 windows and one of these will lose the focus
Try to right click and chose "save target as": what happens?
This problem happens just with the tremulous.megavoid.de website?