When you first install OSX there is that little web link in your dock that takes you to the OSX home page. The icon has the @ on it. Ok how do I get that back? I deleted it but now I'd like to get it back and can't figure out how. Any ideas?
I don't know if this is the only way to do it, but I dragged a Bookmark from Safari (after clicking that little "Show all bookmarks" button) to the dock, and it worked.
...or just drag it form the locator bar (in Safari). Go to the page you want to link up in the Dock, grab the favicon (the little icon on the left inside the Locator bar) and drag that to the Dock. Easy.
Now why it doesn't work from Firefox is more of a puzzle...