WTH? The Mozilla Firefox Web Browser 5 is available for download. Wasn't it only a month or two ago that FF 4.0 was introduced?
Seems to me that they are feeling under the numbers-gun from Chome (currently at version 8 billion) and are adopting a more rolling release cycle, with less emphasis on the major version numbers. Funnily I went to check on my home desktop and found I already had Firefox 5 on it, and hadn't even noticed.