Gotta love it! Firefox 5 is a "security and stability update". No lengthy explanations on why version 5 is better than 4, and an "Upgrade Now" button. User's would want to install this! I also like the prompt I get when one of my add-ons won't work with the new version.
Though it might scare some users from updating, the warning is important. It seems overly intrusive to just update Firefox without it. And the message is short and cannot be misunderstood.
As soon as they are made compatible, Firefox will update and re-enable these add-onsThat's a crystal clear message to the user: The add-on won't work now, but don't worry, we'll fix it for you as soon as we can. The user is relieved of fixing this on her own, and that's great!
So, go get your security and stability update for Firefox if you haven't already.