That link works fine for me from just outside the Bay Area in California -- where are you connecting from? Do you get the same result if you try that link in different browsers?

It sounds like you have uninstalled Firefox so I'm not sure what you mean by "only happens with Firefox". You mean only happens on that URL (which is for Firefox), or it works fine in some other browser but fails when used in Firefox? We have not moved our download site. If it's just that one site that is giving you errors I would suspect someone is trying to prevent FIrefox updates. It could be somewhere on your local network, but blocking only Firefox wouldn't make a lot of sense as an attack unless you're on a corporate network that forbids using Firefox

Another possibility is local malware running on your machine.

If your computer is a laptop you could tell whether it's the first one by taking your computer to a coffee shop or library or somewhere that has WIFI and trying the download from there. If it's still blocked then I would blame local malware. If it's not blocked then talk to the administrator of your network where it doesn't work.

Some protection programs don't like the update/install stubs. Go here for the full installer.

http://www.mozilla.org/en-US/firefox/all/ Download Firefox For All Languages And Systems