Firefox 3.6.2 had been silently released. Some users may actually see a prompt stating that a critical update is available, but unable to download. This is referring to the Firefox 3.6.2 update which address some very critical vulnerabilities. I had not be able to find the exact update file online, but what you can do is to simply go to the download page for Firefox and download 3.6 again. After installation, you will notice that it is now 3.6.2.
On the other hand, Opera has also release 10.51 which address 2 of the high risk vulnerabilities. This should automatically be updated.